I would encourage you to rethink your response. The way you've typed INSANE in capital letters might be very indicative of how you're coming across in real life, not just on the printed page.
The way I see it, you have two really different situations: one set of parents who are very cold and who refuse to even meet two beautiful little children, and one set of parents who are trying to be helpful but who may be a little more intrusive than you'd like or are accustomed to.
It would be normal for you to grieve the loss of your parents' interaction in your life, your married life and the lives of your children. I'd be angry and sad. They have rejected you, they are trying to sue you, they are depriving your siblings of a relationship with you. How sad.
However, for your wife's parents to treat you and your wife and your children the exact same way as they treat their other children - well, that should make you feel joyful! Just think, they have not rejected you, they have not judged you, they have welcomed you and they insist on offering your children the same gifts they have offered every other grandchild. It sounds as though they made the conscious decision to include your adopted children into the family, and the decision to accept a family with two mommies, and that decision should be celebrated and embraced, not faced with feeling INSANE because they have money to offer and do so willingly.
Be thankful! Do not use words like insane. Use words like joyful, appreciative, happy, and loved. Ok, so they pry a little, they are assuming you'll want the same gifts that the other kids accepted. They're treating you like parents, like a family, like the moms of their new grandchildren. What a blessing.
Don't rock the boat too much. But it's ok to try to help them understand that perhaps you won't be sending your kids to the same private school that all the family has attended for generations, but you will certainly be preparing them for college and a college fund would be carefully tended to and appreciated. Tell them when you're ready to purchase a house, you'd love them to give their input and you'll be happy to listen to their advice but right now house hunting isn't something you're doing. Tell them that for now two children is what you're happy with, and that your family needs time to bond, but that you love that they're excited about more children and if and when the time is right, you'll tell them.
Don't think of it as "the grandparents being the ones providing for your kids". Rethink that. Think of how blessed your children are that their grandparents care. It doesn't detract from the fact that you are the kids' mom, that you're providing the love at night when they go to bed, that you're the one who will love them through strep throat and first day of school fears. It doesn't have to be "help", it can be "sharing" or "love".
This is not something to be INSANE about. This is something to feel loved by, and wanted, and welcomed and very very fortunate. Save the INSANE for those parents who won't acknowledge you, want to remove you from your siblings' lives, and who won't meet two innocent children.
Please, appreciate your blessings. Embrace these grandparents and in-laws.