Don't the guinea pigs get ticks and fleas being outside all summer ?
I think putting their cage in a bigger one is the best idea . But you need to made sure there is no way your cat can sneeze it head into the door and if your cat wear a collar made sure it can't get hung onto the cage. If your cat really want to go after the pigs it might try to break into the cage . I had a cat and he tried to knock my daughter hamster cage off a table by getting behind it and pushing it off the table .
