I have done half a dozen cruises with Norwegian, they do assist people with mobility issues to board tenders using 2 crew members.
I have just looked at the FAQ, and they seem to have lowered the weight to 100lbs now. Would need to be a child or very fragile person to fall into that weight range shame this has changed.
I rarely do ship tours, unless the place I want to visit very far and the traffic can be bad. The last ship tour I did was in December for the Củ Chi Tunnels and Ho Chi Minh City tour from Phu My port, which is 80km south of Ho Chi Minh city. I wasn't going to risk it there.
But generally most people should know what they are risking. I've seen ship wait only 1 hour before for late comers. Late departures can affect the arrival time in the next port. Best not to hold up thousands for the sake of a few.