The hatch on the far side is just another way to give them their treats. Suspect I would have a pet sitter use that rather than going into the cages, unless they were really familiar with the different species.
They don't really come & go; they have been living outside for about six months and everyone seems to thrive. If I need to get someone out, there is a people sized door in the back with an atrium "catch" in case they are quicker than I am.
Real good, a hatch on the outside wall may be a problem. If they know treats arrive via the hatch they may escape when opened. Maybe a swivel feeder or otherwise escape proofing is needed. Budgies are very curious and very quick even if not tame.
That is so cool. Tobi would be in heaven..Mind you she does have the run of the livingroom, but some times it doesn't seem big enough to fly her laps...
13 little Budgies wow. I bet there's a lot of chatter going on in there..