I use an old film canister which I have a little calcium dust in there to dust my fruit flies.

What I do to get mine out is tap on the sides of the containers to get them to fall down to the bottom. Then I try and to put them in the canister. I always do this over the tank so if any fall out which they do they get eaten, and not lost on my floor. I'm still able to dust most of them though.

Flightless fruitflies aren't much of a mess. They won't be flying everywhere so your mom won't have to worry about that.

I'd go with a wider tank than taller for them. They really need a good amount of space. The 2.5 gallon is fine for the time being, but if you can get a bigger tank than I would.