You say "we" which, IMO, requires less extreme vigilance. Split the items between you. You won't be stranded if the worse happens, which in reality is unlikely. That being said, your crossbody purse seems fine. You can lock the zippers as you say. I rarely wore/wear a money belt and it wasn't until I started reading Rick Steves way back when and traveling solo that I did. I would wear the leg wallet, but it hasn't worked for me in years. I wear a small, lockable with a clip, crossbody bag. That's the type I wear at home as well because they are so organized and small. When I get to my destination, I leave a credit and debit card with copies of docs in my suitcase. I always carry enough, including my passport, to turn on a dime and leave the country without having to get back to my hotel room.
My small bag for travels is an older, black and with smaller logo than this Pacsafe Tech bag, but it is essentially the same. I wear this with everything except when I need to take it off for security until I'm finished transporting myself. My mobile fits in this as well. It also is flat enough to wear under a blazer or such so unless your dress is skin tight it should work. It easily fits in my personal item or a medium purse if I need one later in my trip although I'm so used to wearing it, I usually just have it crossbody and visible. Otherwise, it is just my purse for my travels as well. Here's Nora Dunn with a review (but I had it first. LOL).
I did meet a woman who wore underpants with a front pocket in the center. She didn't show me LOL, but I've seen them online and that was her solution regardless of outer clothes. This seems to be awkward for security, however.
I once wore a waist money belt once...it fell off in the ladies room right away. Never will wear one again, or anything that can be untied with a clasp. I think most people actually just lose things, but that's just my opinion, and that's why I protect my things...from me.
I did recently buy a bra pocket to think about, but now I can't find it so I guess that was wrong. LOL