@Surprisedbuthappy
Your ire seems to be directed only at the DH and in laws. Presumably because they are the ones with money that they’re withholding.
They (most likely) had that money before OP came on the scene, before possibly/probably the eldest was even born. It’s theirs to do what they wish with, given they (I’m assuming) earned it. Why are you having a pop at them for not sharing it with people they don’t choose to share it with?
Presumably it’s because there’s an innocent child in all this, and she is the one who is going to suffer. But it was her mum who put her in this situation. Not the in-laws (the SIL to be didn’t even know she existed). The fault lies with the mum. If the DH made promises he’s now not keeping (doesn’t seem he is, but if he did) it’s also his fault and he should share the blame.
This really has nothing to do with the in laws. They’re just going about their business, doing their thing. She is not their grandchild.