"I thought they would need me for advice and babysitting" but did you need your mother-in-law for advice? Wasn't her advice the last thing you wanted? you had found out for yourself how to look after your babies, you had medical people to advise you, above all you had your own ideas and opinions. You were not a lesser person being instructed.
We all have to accept that when our children are grown-up they want to make their own decisions, not be still treated as infants to do as mummy says, or to dance attendance on mummy (unless she is alone and incapable of looking after herself.) If you have been a bit too bossy or too clingy in the past, then it is not surprising that two of your three sons are keeping their distance now. They have their own lives to lead, and you will find them far keener to talk to you if you have seen other people, done other things, and have your life too.
As for the baby - At that age they are becoming more aware of the difference between their own parents, who they see every day, and people they only see occasionally. If you rush at them cooing and eager to cuddle them, they try to break free. Well, wouldn't you, if someone threw their arms around you and exclaimed how wonderful you were and how they could just eat you? You would scream and struggle. Remember that he is not a cuddly toy, he is a little person.
He has to come to you. Ignore him for the first quarter of an hour that you are with them, but have something bright and jangly in your hands, and fidget with it as you talk to his parents. After a while, "notice" that he is interested in it, and show it to him and talk to him about it - without touching him. He will put out a hand for it, let him play with it, but don't let go of it yourself, that is your connection to him, and you want him to connect playing with this nice new toy with having you there near him. Keep talking to him, about anything at all, so that he also gets used to your voice. Don't rush it, he needs to be woo'd craftily. The cuddles will come when he knows you better.
Taking it slowly is the answer. If you also take your relationship with your sons slowly and don't try to force the lost intimacy, you will eventually regain it. Your stepping back a bit is working, but it takes time. Keep at it, and good wishes.