Hi @sheepdad it’s my pleasure if I can be of assistance.
I am not an expert by any means so I don’t think I will review and comment on the videos but what I can say about NEC prep is that they have suitable programs for very young kids (Suzuki etc) all the way up to HS seniors preparing for conservatory applications. A large number of orchestras place young musicians according to their levels and also coached chamber music ensembles. Suggest you review their web page and give them a call as well.
Best of luck!!! This is all so exciting.