The shelter may have some information, but I would suggest at least a week in the garage with food, water and kitty litter for them to get to know the new house. If you have or can arrange some hidey places near the garage (bushes are good) so they can be outside but not too far that would help. In the garage itself if there are hidden places (may look like disorganized junk) that would also help because they are likely to want to have cover in a strange place. My feral kitties nap on the grass-catcher bag of the lawnmower, I think it’s like a hammock for them.
Some feral cats I’ve known have become tame after you are around them with no challenge, and then feed them with you close by. Even if you leave kibble (dry food) out you could have a set time to bring some moist food (tuna) and dole it out to them on a dish (large enough for them to share). put the dish at the edge of the garage and stay at the other end after you put it down. Then over time (a month or two) gradually move closer until they are comfortable with you close by. Do this at a set time each day so they get in the habit of coming ‘home’ then.
If you are game to have them in the house (which you may need since the droppings were inside) you can start with them in a room, again, keep food, water & letterbox available at all times and have places they can hide from you (e.g. closet door propped open, box behind a chair, etc.) that will help them relax.
Always give them a bit of notice if you’re coming in to the ‘room’ or ‘garage’. Say ‘hello’ or whatever you want, but don’t just barge in (even though it’s your space). The idea is to make it their space, so if you ‘respect’ it that way they will eventually be calmer.
Kind of concerned about the school to the side, I would try to keep them ‘home’ and make it as comfortable for them as possible. If you have a dog do not let it chase them - would be best to keep them apart.
Good luck, I hope they stay and that you have a couple of good mousers and good company for years.
