The way to do it is to get a lawyer to draft the deed and have it signed, notarized, and recorded.
The implications are BROAD. Being put on the deed isn't like being made a member of a club. Your father-in-law would be giving half the house to you, irrevocably.
There are serious issues. Is this the house he's living in? Will he be needing money later that's tied up in the house? He can not get a reverse mortgage with someone younger than the qualifying age as an owner. It would be hard for him to sell or refi without your assistance. It may also jeopardize his medicaid eligibility.
For you, you will now get his basis which may cause you substantial tax issues when you subsequently sell (after his death). You'd get a stepped-up basis if you inherited the property instead.