Just my $0.02 but its going to depend completely on who he is as a teacher and how much he is willing to pass along and be patient. Given the family connection and what sounds like commitment on your part it would on its face sound like a win-win but it honestly all boils down to how well/interested of a teacher he is, how patient he is, how pressed he is in is current workload to push out work as opposed to diverting time to showing/explaining.
In all the years Ive been doing this Ive unfortunately more often than not come in contact with older individuals who have been doing things the way they have for years and years and may or may not have entertained new tech/advancements in the industry and moreso only rarely been willing to invest in tech, machinery, equipment, that will advance their position (faster which = more money in pocket). They can often times be curmudgeonly which we all can fall prey to when we are afforded a lot of work that allows us to be quiet in our own shop in our own space.
That said, and not tooting my own horn, I would absolutely love to have a young person (or old person) who was interested in it all. I love to teach and share the little I know but even that gets a bit short when time is short and the push is on.
Hopefully he and your interaction is very sharing and open. My advice beyond that would be to keep your mouth shut more than open and stay extremely busy doing anything from sweeping, to re-organizing the most obscure corner of the shop. A lot of your learning will be a long term soak-in rather than it being explained to you. Even if it were explained you'd never get it all in one round which means you'll have to go back for more questions which can be annoying. Its best to just shut your yap and soak, soak, soak.. after the 15'th soak on a subject you'll swear you have it hammered and realize you need 20 more soaks.
Shut up, keep your eyes open, parrot his every maneuver. The way he holds a tool, the way he never walks across the shop empty handed (wasted energy), the what he approaches work with his body, how he somehow seems to move heavy objects with ease while you flounder. Parrot his every movement. Once you've mastered those movements you may improve upon them but dont try til youve licked moving just like he does.
After thats its all wash rinse repeat.... and again.. hope he enjoys teaching.