Thank you very much for your reply. I agree, with a conservative expected inheritance included we are already ~40x FI, but continuing our plans as if we aren't and aiming for 30-35x in ~7yrs. The retirement date is driven partially by benefits rather than investment goals only. If we make it through all 7 of those working years without both of my parents passing, then inheritance anytime after that would push us to increase our expected yearly retirement spending since we'd be something like 60+x and the $ would outlive us with no children, even with significant philanthropy. Estate tax will not apply luckily (unluckily? haha).
I misspoke before - we were actually in the 24% bracket in 2019, and should continue to be until the expiration of TCJA, then 2 years of whatever is in store after that. My parents currently cycle between 22-24% depending on investment income, so working with a moving target of 2% difference probably isn't worth the effort, but as you point out that could jump up to 32-35% when my father has to file single - a much bigger deal. It is difficult for them to estimate taxable income prior to EOY, but I will try and push them get a better idea. Additional Roth conversions this year and next year (if my mom makes it into 2021) may be a good idea, especially if they will be in 22% or less.
Agree on planning in stages. It's obviously a delicate subject with my mom's health deteriorating, but an important one I've been trying to find some time to discuss with them. Not a bad idea to investigate my mom bequeathing to us directly, but they do have a trust setup which might complicate that.
Appreciate the links - I did find the one about GCC Jr which was very helpful, and am trying to comprehend the 401k too large articles. Healthcare is indeed a major concern in general after I stop working (giving up completely free healthcare will be pretty difficult!), and we have more to figure out there with expectations of living outside the US a while as well. We'll worry more about that closer to retirement time. Good idea about Roth conversions post-medicare.
BTW, we have the same plan as you buying a sailboat, which is another reason we are significantly increasing our taxable savings. Boat purchase and 10-20% value in expenses per year adds up!
ASA 101/103/104 complete and doing 114 this weekend, and we have bareboat charters setup for the next couple of years and will continue to do that at least once a year as we finish out our careers! Charter in BVI a couple years ago was a bad idea haha

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Thanks again for your advice!