The best bet is to let the son play the keyboards.
A musical instrument should never be a surprise.
It's personal. The mom can narrow the choices she wants within her price range, but ultimately, it should be the son's decision. That said, many professionals have chosen the PC2X such as Billy Joel and Billy Powell. They are very demanding and were using grand pianos with MIDI. They have replaced those with only a PC2X . I found it very easy to make them happy with just a few program adjustments.
All of the Keyboards you mentioned will do the job.
The selection, in the end, is a matter of the heart and not the head.
My 2 pennies
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Take Care,
Geo