If your son comes to you with an issue with his wife, ask him if he has spoken to his wife about it. If not, send him home to do just that before you hear anything else off him.
Never get involved in arguments between them because they are between THEM. Even if one of them asks.
Don't expect your dil to take over remembering birthdays and Christmas and Easter and any other thing you think you should be getting a card for. Don't blame her when it doesn't happen.
Don't expect her to make a weekly call or whatever to check you're still alive and then get cross with her when she doesn't. Actually when your son doesn't either, don't be cross with her. Maybe you could ring occasionally and not to discuss health issues, maybe you would ask her about her.
The odd compliment on how well she looks, is taking care of things, is making your son happy would be good.
Perhaps marvel occasionally that even though she works full time and has many children, she can still manage to put a home made meal on the table in the evenings. And even if her meal is a ready one, maybe tell her you think she's doing brilliantly.
Let go of your son. You were there first and that will never be forgotten but he has his own adult life that you spent years of yours preparing him for. At least let him live it.
I haven't had a happy time with my mil and I would have wanted something different. I worry it's too late now. Don't start down that route, it's hard to recover from.
Good luck!