Do you have skinny pigs or furred pigs? Normal guinea pigs won't need clothes. Clothes aren't recommended because they can constrict movement and overheat. My 4 pigs survived my house getting down to 42 when we had no power in February and it was in the single digits outside. If they are truly going to be some place cold like that, what I did was move them to the warmed part of the house, cover their cages, give them extra hay and covered their houses so they can stay warm.
If your situation isn't something extreme, then just leave the pigs like they are. They'll be fine.