Legal Question in Real Estate Law in New York

Where are you reading about those terms "lifetime usage" and "lifetime estate?" The legal term for what you're talking about (if I understand you correctly), is "life estate." You would say "mom and dad are transferring, by deed, the house to brother and sister, as tenants in common, and retaining for themselves a life estate in the home." I have to caution you to be very careful here, as this sounds like a good idea, and it almost usually is, but there's also a possibility your plans can backfire. Be careful, and good luck.