Personally, I dislike the ANA IC due to location and stingy upgrade policy. I have friends who consider this their go-to IC, so different strokes for different folks.

IC Strings is likely the best for ease of getting around Tokyo via public transportation for a first-time visitor (access to HND airport, local JR options, most notably Yamanote line, as well as Shinkansen if you travel further afield). Rooms are aged, club lounge pleasant, breakfast excellent. Nothing of interest in the direct vicinity of the hotel, though.

IC Tokyo Bay also has weird upgrade and club lounge policies. It's ok for getting around, but not much in the immediate vicinity. I loaded up on IC Tokyo Bay reservations for 2025, because they have rolling "good deal" points rates when you book at end of schedule. Right now, you'd be looking at steamy summer months, but a while back, I picked up peak sakura weekends for ~33k points a night. If this "good deal" persists through fall, I wouldn't hesitate to pick IC Tokyo Bay over ANA or Strings (which will usually run at 2-3x that amount of points).

Have no recent experience with the Yokohama ICs (staying at Sheraton or Hyatt there), but my general advice would be that Yokohama is an acceptable location for tourists going into Tokyo. Getting from Yokohama station to say Shibuya doesn't take significantly longer than from Shinagawa. For work, I'd want to minimize commuting time, and pick something close.

OP doesn't say whether the elderly parents have mobility challenges. I've traveled to Japan with a wheelchair user -- it's generally a great country for that, with lots of cool stuff like escalators that can turn into a wheelchair platform, cabs that have passenger seats that can fold out to street level for easy transfer, etc. On the downside, many stations are under-elevatored and waits can be lengthy. If the elderly parents walk slowly or use a cane, beware that seating in public (benches etc) can be extremely hard to come by, so not always easy to rest up every now and then.