them radition guns hurt is there any trick to killing them? or tricks to defending

You could put your Hazmat suit on ? (untested)

Kill them quickly...

Stack radiation resistance.

Easiest way is a hazmat suit. Otherwise power armor does a good job, and there's always rad-X, and rad away.

Also i think they're weakest to projectile damage, so shooting them with bullets (instead of lasers or a stolen Gamma Gun) works best.

Decent Power Armour gives good enough radiation protection to mow them down without even bothering to use cover. Upgrade it even further, and the only thing you'll have to fear are the occasional grenade.

A Fatman might work lol

hazmat suit, then they die like like anything else, just make sure you kill anything that does normal damage first, or the low standard armor of the hazmat suit will hurt.,

Kill them before they kill you. And their radiation guns can be dodged, it's tricky but possible.