WIBTA if I intervened?

My FIL recently got a hold of inheritance as his father passed away. My FIL has two daughters - my fiancee and her sister. The inheritance in question is a plot of land with a half built house (foundations and first two floors are set) that will require a lot of work.

Once the funeral was settled my FIL plainly told us that he will continue and finish the house at which point he will give it to his other sister. My fiancee didn't seem too moved by this but I was stunned. I don't see how a parent can be so obvious in his favoritism (something my fiancee has complained about for a while). His reasoning was that I am more successful and that since I already own a flat we will not need one. This is technically true and I may come off as some sort of gold digger, but it is not that. As a father myself I will never be able to reconcile doing such a thing. He is actively punishing his daughter for getting a more successful husband.

Something else to consider is that both we (me and my fiancee) have a daughter that should inherit. Her sister and her husband also have a daughter.

It is important to note that I am currently paying off mortgage, I don't own my place outright. While I am not so worried about me and my fiancee my FIL's granddaughter should receive what is rightfully hers. Would he have acted in this manner if my fiancee was single?

I am well aware that I should not stick my nose in other people's business, but my fiancee stands to get fucked out of a lot of money she deserves just because she is used to being treated like an afterthought by her family. If I intervene I will defend her interests and probably alienate the in-laws. It is important to note that I am not sure if my fiancee will appreciate me stepping up for her.

So, WIBTA if I speak up?