Well, I'm only 5'2", and even if I lose 30 lbs, I would not be "thin"! Let's just say 30 lbs would be a much healthier weight!
My kids are 5 and almost 2. We are borrowing a trailer, which we love, and are looking into a trail-a-bike for the 5 yo. If you are considering a trail-a-bike for riding with one of your kids, one thing to know is that almost all of them attach to the seat post (except for the wickedly expensive burley piccolo), and that most comfort bikes come with a suspension seat posts for a less bumpy ride. So you have to make sure there's enough of the non-susp part of the seat post exposed to hook the trail-a-bike up to. You probably won't have a problem with that, since you're tall, but keep it in mind if you think you (or your wife) might use a trail-a-bike someday. You can always replace the suspension seat post with a non-susp one, but that'll be extra $$.
I can't decide what to buy...so I'm holding off. I rode my late '80s 12 speed road bike for about 30 minutes tonight and couldn't hack the hill on the way home. I am pathetic. I need those granny gears! But I'm also cheap, so I may try to make some replacements on my old bike (straight handle bars, maybe new shifters) and eek it out until I can justify the bucks after buying a trail-a-bike and a cyclocomputer. We also need a bike rack for the car. Also, I'm hoping to get my hubby out there too, so we can all go out together on the weekends, but he doesn't have a bike at all. I think the trail-a-bike & trailer will really help me get out there, because I can actually take at least one kid with me, so I don't have to find time to ride at night after my husband gets home. And the kids loved them on vacation.
Your plan of a comfort bike that your wife will also be able to ride is very good, as long as you are both comfortable on it. If that's your plan, you might want to consider bikes that have a low top bar, but not the step-through woman's style. That way if it's a little big for your wife, it won't matter as much b/c that top bar won't be in her way.
Good luck!