Osprey can be researched without a proper lab, although it's probably a pain to do that due to its research time.
Manor air defences can be diverted if that's what you're having trouble with. Or killed off, but you likely don't have actual interceptors with weapons worth the name yet.
If it's still a baby manor, it'll only get worse, so better get it when it's still young. Baby manors can be identified by them having no actual aircraft (fixed wing or rotary) serving as interceptors. Even if there are rotating blades involved, it's still a young manor and should be killed off before it grows worse.
Manors are not that bad, depending on your difficulty level and tolerance for reloading. If you want to have no margin for mistakes, it can be a bit hard. But a Dragonfly's worth of troops and a reload or two can absolutely take a manor, at least a tier 1-2 manor, especially if it's one without enemies who have grenade launchers (or Deep Ones Gillmen)