[cypher]

Aw! they are lovely
As Drago said two of everything & no levels or areas they can easily become territorial over are important to try to keep them living happily together.
Behaviour to look out for is generally a big difference in character, if one is out a lot but the other is usually hiding away that can be a sign that bullying may be going on also if you see one chasing the other a lot, a big difference in size/weight/condition can mean that one is preventing the other from getting sufficient food.
Squabbling is normal to some extent but if squeaks or screeching become frequent, louder or really high pitched then small squabbles may have reached the point where they have fallen out & need to be separated.
It's not easy to describe how things might change but as you get to know them it becomes easier to know if they are both happy or not really.