DIL parents live with my son/DIL-I feel left out

This seems a very strange story who owns the house they all live in?
How can your son hire a ‘maid’ he cannot afford ?
Is your daughter in law working why can’t she clean and feed the family ?
I m guessing this story isn’t in the U.K. ? Or is it!
What age are the children can they come to you for a weekend or a night ?
Is it you that hates this situation are your son and daughter in law comfortable with it, that’s the main point if they both are then you just have to put up with it, if they aren’t then they have to do something themselves

I dont get this, you say your son hired a maid, do you mean a cleaner, or someone who is there every day waiting on the family?
I can understand you are upset but it's your son who is doing the enabling, also you say he cannot afford the maid, but he is paying for one. Its clear the family wants them there for some reason, do they do childcare?
Also you cannot blame the other Grandparents for your relationship with your son, that's between you and him.
You do come across as jealous, which I can understand, however it us not an attractive quality. Please leave well alone and enjoy what you do have, because if you dont you are stiring up heartache for yourself.

Invite your son over to your house occasionally?

I'm guessing your son is comfortable enough with the situation or he would put a stop to it.

If you want to see them alone, can you invite them to your home for dinner?

Your son and dil choose to live with her parents, who are clear moochers.

Is it right? No, but there is nothing you can do

"I go to great lengths to babysit and help out but I can't be the grandma i want to be while they live there. Ex; I love to make them dinner, but then I have to cook for the DIL parents too. I'd also like to spend the night and see the GC to bed etc."
Does your grandma role match your son's and dil's expectations of what a grandmother should do?

Re: spend the night - how far is your son's home from yours?

Wanting to spend the night to see your gc to bed is a parents' role, not grandparents.

"the DIL parents have almost destroyed my relationship with my son."
No, your son has almost destroyed your relationship with you