White-rumped Munias as Pets

Received some white-rumped munias (not bengali munia) as pets. Any suggestions on how to care for them would be greatly appreciated.

Currently, I'm feeding them millets. I'm somewhat concerned that they may be overeating, and also having watery stools. What diet is suitable for them?

There're six of them in a relatively small cage, and they all tend to huddle together most of the time. Should I get them a bigger cage?