I don't want to leave LO overnight yet

No I wouldn't agree to her having the baby overnight just yet for all the reasons given above. She should know better especially with an untrustworthy dog.

With a dog like that id say no to day trips as well, because if they're out for the day and go back to house for any length of time, then the dog could still attack even just in a short time, if MiL popped to loo or something??No youre not unreasonable, just refuse.(maybe when the dog has eventually gone to doggy heaven(or hell,in his case?) I would tell her)

Lesim, don’t even let them have your child for the afternoon if there’s the slightest chance they would take him to their house!!
You’ll never forgive yourself if the dog takes a chunk out of your precious child, for your own sake, as well as baby, DONT allow it! ???

Well apart from the possibility of your one-year-old getting mauled by the dog and the fact that he might come back extremely insecure as he doesn’t know his grandparents very well it’s not something I would do no matter how wonderful my in-laws were or even consider. They are being extremely unreasonable.

The dog is jealous and therefore dangerous. The house is not safe for your baby. You need to get advice about the dog from a dog expert. I think it is highly likely that the dog feels it is the top dog and owns the house and will never give way. My sisters son and DIL had to send their dog back to the breeder after their dog bit their child in the face. He is now hyperactive from the stress experienced as a baby in the household.

Put your family first and if it doesn’t feel right, then just say it’s not an option and you will reconsider when your child is older. Our grandchildren did not stay over on their own until they were 5 or 6, and then only after they had visited with their parents loads of times. We left it to our daughter to decide when the time was right.
Also your MIL needs to consider whether her dog should be there when you visit. I love dogs and have one myself, but we would not put any child, (and the dog who could end up being PTS)at risk if there is a history or aggression.
Suggest you set out clear boundaries at the outset.

Reading through these comments it's pretty obvious that the majority vote is that the OP is definitely not being unreasonable, to which I agree whole heartedly. It always amazes me that so many grandparents think they have rights over their grandchildren and can decide when they can take the little ones.

Surely it's a privilege and not a right to be able to have a small child overnight?

Susan56 said it correctly. Your baby, your rules. Stick to your guns. Wrong in so many ways - angry muzzled dog and Covid. You do not want a traumatised child that will stay with the child. You are not being unreasonable. MIL has the problem.

You're not in any way being unreasonable.
The dog is reason enough. How can she expect you to leave a small baby with her when she acts so irresponsibly.
She shouldn't be insisting on anything!

Your child your rules. Especially with the dog situation.
If she’s silly enough to fall out with you about it it will be her loss. Hopefully it won’t come to that though.

No way should you leave a one year old with someone he hasn't yet got to know - with an aggressive dog. You would never forgive yourself if he got hurt and you have not yet seen that Mil can care for your child as you would like. No need to fall out. Just point out that in these difficult times things have changed. Carry on saying that is still early days. You feel that your baby is too young to be left. End the discussion here. I wouldn't leave a child or baby at any time with someone who had an aggressive dog Ever.

Don't even think of it. Your instincts are telling you to protect your child. Listen to them.

Your child comes first. The fact she won't even put the dog, who has proved to be aggressive, in another room when you visit, I find really alarming. What kind of a grandmother is that?

As long as she has a dog the answer should be no

Your plan sounds well thought out. The dog even if muzzled could still be a problem with the claws. I have had dogs for years, terrier types and no way would I permit any of them near my grandchildren when they were so young. The fact the dog in question is muzzled should raise alarm bells. Insist the dog is kept in another room when you visit.

Definately do not leave your child there, it is too young, and its definately unsafe with regard to the dog, there is plenty of time when they both get aquainted, the Mum-in-Law and your child.

No you are not!
My mum had her grandchildren overnight from a few months old - the first one at 6 weeks old, while my sister in law was in hospital - but she had spent time with all of them from when they were tiny.
The fact that your DS has hardly seen her for months , along with the problem with the dog, to me, means that you are being wise not to allow him to stay.
Regardless, she needs to train her dog not to snap and if that isn't possible, the dog should be put in separate room when you visit (which may well make that problem worse).
You have given her the option of her taking him out for the day or on little outings for an afternoon but she doesn't want that.
Your child, your choice. She has to accept that rather than try to bully you into doing her choice. Stick to your guns and I'm just waiting for the post saying " My DiL will not let my GS stay with me AIBU " !

As a MIL to a DIL, no you are not being unreasonable. When our first GC was born DIL seemed to trust her mum more than me, it upset me but of course she was going to go to her mum more. I cannot remember what age they started sleeping over but pretty sure it was over a year. You are right to start with a few hours and build up. That of course is not taking into account the dog. Sorry but unless they are prepared to keep it well away from your child then it must be a firm but regretful no. I do not have a dog now, but had an older dog when our youngest was small. The dog became very possessive of me as she aged to the point where she would yap at people who came close including the children. Much as I loved my dog my children's welfare came first, she was the same height as our youngest and I would never have forgiven myself if something had happened. If they are caring grandparents they should understand your concerns for their grandchild. Hope it all resolves amicably

Your child your choice,end of.
She sounds like a bully too.
So on that account alone forget it and her.

I don't think that you are being unreasonable, but ultimately that isn't the point. You are the parents, what you say goes. You are legally responsible for your child's welfare and you don't have to justify your wishes. You don't have to explain, compromise or alter your decisions, and you don't have to visit at all.
eg "would you all like to come over for the day/"
"will the dog be there and running about?"
"yes"
"no"
"why not? the dog is fine, it's my grandchild. it's not fair, the dog isn't dangerous"
"I'm glad you enjoy your dog. We're not coming"
"why not?"
"because of the dog"
"but why not"
"I have to end this call now"

You are not unreasonable Lesim99. Just say " No thank you, but I do appreciate your kindness".
Perhaps keep your options open, as these grandparents some time in an uncertain future may be what you need.

It's true what other grans are saying about the dog. In the meantime, can you try to educate the grandmother about dog safety perhaps along the lines of the experienced advice from 4allweknow?

No your being sensible caring parents never let anyone emotionally blackmail you.

It’s your MIL who’s being unreasonable. I wouldn’t leave your wee one with her unsupervised at all until he’s much, much older.

YANBU.

Aside from the fact that this is your DC so you decide if and when he stays anywhere he’s still a baby, so this applies even more so.

The clincher for me is the dog. Even if your DC was Secondary School age I wouldn’t let him stay in a house where there is a potentially dangerous dog, not even a small one.

Politely say no and stick to it until you can be sure that your child is safe staying there.