I am not a real estate guy and I don't know Illinois law. This would be in Chicago. Unmarried domestic couple plus father in law (FIL). Younger member of couple has not bought a house and is associated with institution where she can get excellent financing. Older member of couple has income stream and resources sufficient to buy house alone, but not really a job or history in Illinois, so financing might be odd or more expensive. FIL could write a check for a house and wants to help.

Younger member of couple wants to build equity in a home. Older member doesn't care. FIL is old and doesn't care.

House would be cheap enough that mortgage interest deduction is a consideration. Consider total income of the couple to be something like $100,000, unless the older member gets a full time job (possible), which would bump to 150,000.

Suggestions on how to do this? FIL loans down payment, takes a note that is second in priority to mortgage, house titled in both names with buy out provision and method of calculating contributions? I am just making it up. Seems to me there should be some kind of standard system.

Our concern is for the ownership to be totally fair and transparent, with clear path forward.

Another method would be for FIL to buy and rent to the couple, with a rent to own type agreement. Don't know how that works as far as taxes.

Way out of my comfort zone on this stuff.

Thanks.

TL:DR/ Couple wants to buy house but plan for death, split up, sale of house, all eventualities. FIL can help with funds. What kind of agreement/arrangement would be typical and work?