I was a primary TA and taught 'informal' music groups for recorder, keyboard and percussion, over a twenty year period.
My main instrument was drums, and for forty years I played in amateur bands and stage shows. In addition, I learnt electronic organ in the 1980s.
One of the problems, I think, with learning music, rather like Numeracy at school, children are told and shown what to do to make progress, but aren't really told how to UNDERSTAND WHAT IS REALLY GOING ON.
Music is governed by the laws of Physics and Maths, not by things dreamed up in Italy in the twelfth century!
The Treble and Bass Clefs are NOT two different things, they are both part of The Grand Staff:
www.essential-music-theory.com/grand-staff.html
If you, and he, can study the above link, and try to understand as much of it as you can that should get you started.
DRAW the two staves on plain paper, with a RED line between them; this red line is the ledger line on which sits the note C, BELOW the stave in Treble, and ABOVE the stave in Bass. Now try and mark the positions of all the other C notes on both staves, and you should see they make a pattern, balanced about this red line.
As for doing the reading practice, I guess do 5 or 10 minutes of Treble, then 5 or 10 minutes of Bass, until it starts to become (hopefully!) automatic.
Also, don't worry TOO much about the names of the notes; the important thing is for the fingers to be able to go to correct place on the keys.
[I'll come back in a few days and see if any of this has made any sense to you both, and see how he is getting on.]