Gosh, this has all got a bit personal and besides-the-point.
It's clear to see that some people take on stepchildren as their own, and some don't. Neither is morally superior, in my opinion. You can't force feelings of parenthood - and this really goes to the heart of dark, murky thoughts we all have or might have about how things are with your children versus other people children. The sort of thoughts that make some people do everything possible (legitimate or not) to avoid their own sons going to war knowing full well that means someone else's son will, while other parents would be prepared to go to jail as conscientious objectors to try to protect the lives of all sons (an actual example from my wider family).
If you come from a family that has little to share (eg my maternal side) it's very easy to welcome all and sundry to the bosom of your family. Nobody loses anything (there's nothing to lose), everybody wins something (love, companionship, another loving relationship).
If you come from a family that has a lot to share (eg my paternal side), you have to be very deliberate about how and who you welcome. NOT because you're rich and you want to hoard all your gold coins for your bloodline. Because with privileges come responsibilities, and you have responsibilities and duties to the people you chose to foist the consequences of your actions on. IE your children and their children. If there's millions to go around, 2 DC, 4 GDC, nobody really would notice another child (step GDC) getting the same or similar amount to the other GDC. If there isn't quite that much money; if there are more DC and GDC; basically if adding one more step-GDC means taking away meaningfully from your own GDC - well, what would you do?
This DH and these DGPs haven't completed their families. There's literally a wedding on the cards, this family is in its growth phase. How on earth can the DH say now that he's going to pay for private schooling for his step-child, when he doesn't know how many more children he's going to go on to have?
And whichever poster it was above who implied or even said that being rich automatically means you're an asshole: all that that attitude displays is your own limited life experience. We have wealth in our family. We have step children and step-grandchildren. Under no circumstances would any child be excluded from a wedding. Absolutely would step-children and step-grandchildren be excluded from a photo my grandmother wants of her kids/grandkids....but then we would make sure there are other photos of everyone together. No the step-kids and step-grandkids aren't inheriting anything. Yes the bio kid who has those step-kids has been left whatever amount they would have been left anyway and their prioblem now that their DC are or aren't going to get as much as their cousins (in reality they see the smaller pot for education and housing a quid pro quo for having more step- and half-siblings). I don't think this makes the elders assholes. It makes them people making choices as best as they can, seeking to do the least harm to everyone, bio descendents or not.