Yeah, like Jaysee said, they will eventually get big enough to eat the danios. Their mouths are HUGE in proportion to their size, and anything that fits in it is fair game. When I got mine, the people at the LFS told me they were timid and hide a lot, but mine is always out and about. He's definitely the boss of the tank; my gouramis keep their distance. And unless you plan on upgrading the tank, 29 will be a bit small for a pair of them.
They are very cute though! Mine is definitely my favorite fish.