Owner Financing house to family member

Currently I'm renting my old house to a family member. Originally I was planning on selling the house but he really liked the location and house itself but felt he is too old to take a mortgage out (65y.o.).

One year later he is itching to make improvements and his wife likes the house a lot so they want to purchase it. I told him I would sell it to him under market value 230k (about 20k-30k off). We still owe 60k (3.5%apr) on it. But there is a catch.

The catch is he would prefer to avoid interest and pay it off in 2.5years. 50k down +~6k monthly directly to me. The simplicity of it sounds nice and his income is high and somewhat passive so there is not much worry about him paying it off. I'd imagine upon completion of paying 230k we'd have paid off our loan and transfer it to his name.

It all seems a little too good to be true...Like... Am I giving up a lot or paying more tax wise for capital gains/income tax?

In reality he is saving maybe 8-10k in interest if he got a 10yr mortgage from a bank and paid it off in 2.5 years. Is that worth the process of a non traditional sale like this?