Guinea Pigs Social Life
It is perfectly fine to put two pigs together, in fact it is very important that pigs be kept in pairs or more. Make sure to find a rescue or shelter, or from a reliable.non-breeder from craigslist. Also, make sure they are the same sex or one is neutered/spayed.
If you have a male, they tend to get along better when they are different ages anyway. You MUST have at least a 2x4 grid cage for two males or I can almost gaurantee that they will fight. Bickering is normal at first as they will need to establish doiminace but DO NOT remove unless blood is drawn.
Also, before you introduce a new pig make sure you QUARANITNE for three weeks to make sure the new pig isn't sick and possibly passes it to your old one.