There are a couple issues with keeping guinea pigs around parrots. The pigs should not be any threat to the bird, but large parrots can do a lot of damage with their beaks. Even a single bite could result in a guinea pig losing an eye or worse. Also, there is some danger of disease transmission if the guinea pigs are exposed to bird droppings - like if the parrot was allowed to free fly in the same room and pooped into the open enclosure. Loud bird noises and the sight of a large bird passing over them would also be stressful for the pigs, but they can probably adjust to that over time.
If they are being kept in a different room with minimal contact, I see no problem. But if you allow the parrot in the guinea pig room, you will need to be very vigilant to watch for any signs of aggression or too much curiosity from the parrot and be sure to clean up any poop immediately.