Termidor, these outposts aren't full fledged alien bases (as Dioxine pointed out, every faction gets a custom base layout), Hunting party (8 gals, immune to detection) is enough to take the smallest ones out. At the start you need to blow up a small turret or two, then use a hammer to break the outer wall, and then simply shoot inhabitants since most of them are melee. The only trouble is high caliber turrets, but ninjas drop EM grenades which oneshot them.
If you aren't sure that you can, with them being so close together you could build a base inside their range with 2 hangars, trigger interceptors with a random craft and land, wait until they return home, and send a proper invasion party during interception cooldown. Since every base gives millions in loot, it will be worth it to build a base just to abandon it later.
alternatively-alternatively, your codex craft most likely would be able to reach the base before being spotted, and returning from mission crafts are damage immune.
For t2 and t3 outposts you could bring a bunch of mortars from crazy Hannah and burn them down from afar.