It's hard to know why your lawyer would suggest putting that out there upfront without knowing how the other side is going to be about things that are clearly yours. I have been involved in many negotiations where one side is eminently reasonable and the other side digs in their heels and fights everything.
If money is an issue and the other attorney has a reputation for being reasonable, etc. I could see situations where it might be beneficial.
Why not cut to the chase and just ask your lawyer why the suggestion was made.
Gift letters are common and are used for the benefit of mortgage companies to ensure that the borrow doesn't also have to pay back a portion of the downpayment, which could affect the debt-to-income ratio. I would not be surprised if people challenge them on that basis. Of course I'm sure the other side could get affidavits, declarations, etc. to the extent of the gift.
You should be getting back anything the community (assuming a community property state) contributed to the value of the house. Downpayment monies, mortgage payments, increase in value, etc.
Also, depending on how much the house is worth, I'd be wary of agreeing to anything that gives the FIL the first $50k. What if the house is decreased in value. Why should that "gift" flow entirely to your H.
Please discuss this stuff with your lawyer so you understand the rationale.
This is such an important thing, you really need to make sure that you understand things as you go along and are as good with them as you can be.
