I too commend you on your efforts to assist your parents, and steering them to a trusted LBS is most important as well.

I am older than your dad, taller and presently heavier, I love my comfort bike, a 07 Specialized Crossroads -

I also, learned on my own, a Brooks seat was more comfortable as well, starting with a Brooks Imperial, which is now on a vintage road bike, then placing a B68 onto this bike. Soft and comfy to the touch is not the best to ride, proper firm support of sit bones is important.

Allow parents to learn at their pace, after selecting their own bike (s), and matching bikes may be cute, yet may not be the best for each of them.

It also can be addictive, when I got the Crossroads, my Schwinn Conti was hanging in the garage, now it is out and about as much as the Crossroads, plus I added a 73 Super Sport, a 76 Superior, and another Conti, a Varsity, a Traveler (2 different models), and a few more. Nine total in full ride ready condition, and when wife and I travel, it takes me longer to choose the bike for the trip, (she has only the one), than it does for me to pack.

You may be openning a whole new world to your folkes, enjoy the ride.