Guinea pigs need a constant temperature so should be housed indoors :wink:
BTW I looked around your site, the guinea pigs should have limited pellets, and not that p@h museli mix or whatever it is, I have been telling you that for months, please, please change them over to good quality pellets, like Science Selective which can be widely found throughout the UK and when they are adults limit them down, the majority of their diet should be good quality hay.
Also, howcome your pigs are now outside? :?