[@ArenaSnow] I was thinking bashing their heads in constantly until they stop breathing.

but heres a good list of alien weaknesses.

1 bullets (joke)
2 Being allergic to peanuts
3 once in a while they have to take a special pill in order to keep breathing air.
4 Pepsi. not just any drink. pepsi makes them vaporise. (Yet another joke)
5 The aliens have weaker bones due to living on a low-gravity world from time to time. making them extremely crappy in fights
6 Religious overzealousness. basically each member is extremely religious. not much of a weakness.
7 If you take a vial of their blood and attempt to burn it. the blood will Move away from the fire.
8 seriously smashing their head in with a bat is the biggest weakness
9 Each of the aliens rely on electricity to survive. but not just any electricity, electricity from their all-holy generator.
10 each member pronouces the letter zed as zee instead. 
11 JUST SHOOT THEM WITH A GUN?
12 allergy to jelly.