All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
You should advise those friends not to take an interest-based loan and clarify to them that this is forbidden as it is authentically confirmed that the Prophet said, “Allah has cursed the one who consumes interest and the one who gives it to others.” [Muslim]
The one who gives interest to others is the borrower who pays the interest, but if your friends insist on borrowing money (with interest) and participate with you in the construction, then the prohibition of that loan applies to those who borrow money with interest while there is no sin on other participants, and they [the latter] are entitled to benefit from their apartments in this project.
Allah knows best.