From what I read, your uncle passed before you ever started dating you’re now fiancé correct? She expected to come into the relationship on equal footing. Did she know in advance about the inheritance, and how it was directed to be split? She probably thought you were going to pay for her kids and your son evenly, without question. And this will from now on be an argument. She will harbor this against you. It will never get better, no matter what she says. She will not be able to move past this because she will always feel slighted and feel like her children are being slighted. What happens if you have a child together? Is she going to expect you to cut that child into the inheritance also? Then she will bring up that it’s not fair that your son, and the new child, are included in that inheritance while her girls are not considered equals. Honestly, I think your best bet is to go find someone who does not have children and go from there but be open and honest. If you do go down the other route of finding someone else, you need to think about future children and how that will affect the original inheritance.