Reporting for (PTR) duty!
(Right after my wife, apparently. I swear I didn't follow her here.)
Such awesome plans so far! Except for the couple of family conundrums, those are pretty sucky. But I think you're very right - the moment something big/serious happens in people's lives is when everybody has their bit to say, and typically, it's unpleasant. But I do hope everything goes off smoothly for you, because you definitely deserve to spend your Disney wedding/honeymoon enjoying yourself, and having a great time with the people you care about, not worrying over other people's pettiness. I can definitely sympathise over the in-laws situations, too. Everybody was definitely not onboard from the get-go with mine and Amber's relationship (though some of them only found out after we were married, tough luck), cause, you know, the gay thing. Things are much better now though, so you know, there's always hope

Maybe in time they'll get over those things that they feel are so big but in the grand scheme of things really shouldn't be any more important than the fact that their son is happy.
Btw, I don't think there can be such a thing as going easy on food when at WDW

Okay, some people manage it - we have in the past. But ADRs are just so fun to plan, and before you know it, you just have a ton of them. They're sneaky like that. We're honestly torn as to what we want to do next year - stay at a Value and go wild on food, or stay at a higher level resort (not sure if we could splurge on Deluxes but that'd be the dream, otherwise we'd be good with a Moderate) and go easy on the food. It's a much harder decision to make than it should be.
Also, I gotta say, props on the taking up running thing and signing up for the marathon! We've talked about it now and again, but honestly, I'm pretty sure I could manage to run a whole 2 minutes if my life depended on it, so your two eight minutes with only five minutes of rest/walk in between is super impressive to me. As is going to the gym 5/6 times a week. I've been trying to get in shape but I always get so discouraged and it's really a vicious cycle, so if you've made it that far already, good on you - once it's a formed habit, it's so much harder to break.