As you are from Weston-S-M I asssume you know this, but for anyone reading this who is confused the Balmoral referred to is presuambly the vintage steamer Balmoral which does day trips in the Bristol Channel, not the Fred Olsen cruise ship Balmoral! To answer your question, it's a couple of years since I went on it, but I don't think all decks would be accessible. Also, to embark at Clevedon it is necessary to negotiate several flights of open metal stairs, so a lot of assistance would be needed. However, they may make arrangements for disabled people, so I suggest you go to website www.waverleyexcursions.co.uk.
Well done, good information, I am sure the majority of us had no idea how to answer this confusing (to us) question. ... Neil.