Hi
I am very sorry. What a nasty surprise!
Additionally to the measures already mentioned, I would strongly recommend to remove any bowls from the cage and sprinkle feed veg and pellets around the cage once or twice a day in portions that can be eaten in one go by your piggies. Bowls with uneaten food will be irresistable to mice and can promote the transmission of illnesses.
Keep in mind that hay and fresh grass is making over three quarters of what guinea pigs eat in a day and that any veg, fresh and dry forage, pellets and any treats all together only replace the supplementary role that wild forage used to have.
Also make sure that you keep any human food in closed cupboards at all times. Mice can get through any hole you can push a pencil through.
Ideally, you move your piggies to another room for the time being (even if it means a smaller cage space) and keep the doors to the mouse infested room and to the room you have your piggies moved into closed at all times.
Contagion - Inter-species transmission and pet care during owner illness/pregnancy (incl. Covid)