Just some Spire Shenanigans

Are they hard

Meh. Mostly annoying

Do they respawn?

Nope. The small ones that shoot lasers respawn, but the big ones (=Banshees) do not.

Which weapons are the best against them

On foot I would use 2×Executioners w/ Extra Ammo and Stowed Reloading. Using 2×L6 with same mods might also work. But personally I would recommend to use AX Missile Racks from the Ship and just missile-spam the banshees.

If you're there to farm orthrus, you would want to do this in a group — when starting out you would want to bring a Conda w/ 6×AX missile racks and clean up the banshees. I say Conda because out of the Larges it has the best convergence.

But ye.. just missile-dump the banshees, once done with that kill Orthrus until you run out of ammo, then have someone else from the group keep the instance alive and go pick a more reasonable ship.

I can highly recommend an FDL w/ 4×Modified Plasma Chargers and 1 fixed LR TV Beam.