Yeah I've fallen off the BJJ bus lately (our studio closed for a while and when they came back their options never worked with my schedule, then COVID hit), but as soon as I can get back into it I'll be working on it again...never progressed to far, was decently close to a blue belt when I left, but still learned a huge amount and was able to apply it decently well when sparring.
Sounds like your nephew is pretty legit though, props to him and to you for sticking with multiple disciplines. :)
Nice! Yeah we did the same here in MT. It's nice.