Just that ^^ really :)
DS plays guitar and oboe and has a reasonably good keyboard which he uses for tinkering about. He has recently started studying grade2 theory and I have been advised that higher grade theory is easier for those who play the piano.
Given that he really enjoys music, has good motivational skills and a keyboard ready and waiting, would it be fairly easy to pick up using YouTube or a book? Or perhaps look at casual lessons occasionally as he's not after picking up a third instrument full time and DH would have a fit at the cost!