Should I just go home?

To be honest I would be going home and keeping in close touch. Sometimes things improve when you do not actually live with someone. If you have real concerns about the 11 year old perhaps you should report it but that would be an absolute last resort.

An 11 year old with a sixteen year old boyfriend (over whom his parents have no control)?
Hmmm.
You are right to be concerned but I have no practical advice, other than perhaps stay if you are able until the children are back at school.

It's not the 11 year old too involved the 16 year old - it's her mum!
Messy. Go home.

I would worry too.
How does the 11 year old feel about having the 16 year old boy in the house such a lot?
They seem to be taking attention away from her when she might need it.

Can the 11 year old daughter come to visit you? Maybe for some of the summer?
Or are you afraid what might happen between him and your daughter - which would be odd but not illegal?

Eazybee you ve read that wrong it is a bit difficult with all the initials but it’s the grandaughter who died s boyfriend who is cosying up to the mother not to the 11 year old

As it’s the summer holidays why not ask the 11 year old to come and have a holiday with you and sit the mum down and tell her that in her grief she has transferred her feelings over to the young lad inappropriately and needs some help and grief counselling she may not realise what she is doing unless of course it’s more than you ve written

Yes I am perfectly aware of the relationships but my concern remains with the 11 year old who is or was considered to be the girlfriend of a 16 year old, even though some form of relationship is developing between the mother and this boy.
Seems to be a rather dysfunctional household and Grandma is right to be concerned.

I agree with BlueBelle, could you suggest taking the 11 year old back with you?
As for the other situation, M could be allowing herself into a situation where, if matters took a turnabout she finds herself accused of grooming the boy.

eazybee the 11 year old doesn't seem to be involved with the boy?
I don't understand what you mean here?

Genuinely confused. Sorry

eazybee

Yes I am perfectly aware of the relationships but my concern remains with the 11 year old who is or was considered to be the girlfriend of a 16 year old, even though some form of relationship is developing between the mother and this boy.
Seems to be a rather dysfunctional household and Grandma is right to be concerned.

Eazybee
Still wrong. T is the granddaughter who died. The OP wrote Ts boyfriend of a few months has become closer to M
No mention of the 11 yr old being involved with the boyfriend.

I'm thinking your daughter is depending on the 16 year old too much and he is likely doing the same as they are both grieving for your GD. I think the concern is for the 11 year old GD and yes, as we don't know the 16 year old boy...there might be concern from some that he might have influence over the 11 year old. It is natural that he and your DD would find comfort in him being around, to a point...but I think your DD needs to understand that she needs time to grieve with her 11 year old daughter. And to encourage the 16 year old to move on too. However that is tricky if he is living there? and he doesn't sound like he has a supportive family of his own. Continue to encourage counselling for herself and her 11 year old daughter.