Wash branches and perches. Clean the sand trays. Some soaps and detergents are harmful and sometimes deadly for exotic finches. If you want to use a cleaning aid on your cage, check with your local pet store. There are some recommended disinfectants, such as Oxyfresh Gel' out on the market.
Some people use bleach in their wash water.
I don't, I have heard that even the fumes can be toxic to these little guys. This is a list that I found of birds that can be housed together. Of course there may be personality conflicts depending on the personality of the individual bird. Birds have different personalities, just like humans. During breeding season, most of these birds, defend only their nest area.