There isn't any way to twist the buckles. They funny thing is it seemed tight when I installed it, I checked at the belt path. I was tightening it by pulling the adjuster strap down, and we never would haven't known there was a problem if dh hadn't tightened it. Here's a pic of the buckle, please ignore the crumbs, I didn't get time to vacuum today.
It sounds like you've got two things going on here. First - your dh could be "messing up" your install by pulling up. The carseat is held in place partly by the fact that it's compressing the vehicle seat. If he's pulling up on the adjuster, he could be lifting the seat enough so that your install loses that compression. That's not a sign of a bad install, it's just a sign that the seat is being "shoved around" in a way it's not meant to be. Keep in mind - you're not bolting it to your car when you install it (much as we all wish that were possible!)
Second, your buckles appear to be "forward of the bight." (Meaning, they are in front of the seat-crack.) If you shove the carseat
back while you're installing (into the back of the vehicle seat), your buckle will end up ahead of the belt path, so when you pull on the adjuster, it pulls the carseat, too - because of that gap.
So, what you do to fix that: When you install with the seat belt, set the carseat in the vehicle seat so that the beltpath and the buckle are lined up evenly. Then, while you're installing the carseat, push it straight down (not back). You'll wind up with a small gap between the carseat and the back of the vehicle seat, but only at the bottom - most of the back of the carseat will still be against the vehicle seat. Looks like this; see the little gap at the base of the seat between the carseat and the vehicle seat?