We're also going in December 2020 and have 7-day hoppers, and I'm having trouble planning this far out (and we always book this far out and I love planning!). Since they decided to do boarding passes for ROTR and no Fastpasses have opened up yet for MMRR, it's hard to plan itineraries so far out because we don't know how they will handle rides 11 months from now. It's not as easy as just booking the parks with hard to get rides at the end of your trip. Because it's so undetermined, for the moment I'm basing our parks on where I think Extra Magic Hours WON'T be (we stay onsite but avoid them), and where we want to eat lol.
Do you like to hop often? We hop almost every single day of our trips, but we like the change of scenery. Are your parents pretty mobile? And have they been to WDW before? We traveled with my in-laws for the first time last year and boy did it change our plans, because as much as they wanted to, they could not keep us with us and they ended up not be able to handle a lot of the rides we like.
For HS, I still think it's doable in one day, but who knows...if they change to normal Fastpass and waits, you could be in line for hours. Are you making droids or lightsabers? That eats up a little time but it's not crazy. I'd give it a day and 1/2 to experience it all, or to come back and ride something twice! I would of course do MK twice AT LEAST. You're there during party season so keep that in mind for when to go to MK.
Also, if you're there 10 days, why only a 7 day hopper? Adding on days at that point will be like $10/head per day. It's nice to have the flexibility. But we go to parks on our arrival and departure days.