When I got home from work today and checked on my finches (2 male zebras) I could only spot one (Henry) right away... Closer inspection revealed the second finch (Chester) cowering behind a toy on the floor of the cage

I gave them some fresh millet, and it distracted Henry long enough for Chester to resume his position on the bottom of the cage, but every time he tries to fly back up to one of the perches or to a food dish, Henry chases him around again for a bit before he goes back to the millet. I feel awful for Chester, as Henry is becoming a bit relentless in harassing him

I've had these birds for just over 5 months. They were both very timid and paranoid when I first got them, but Henry quickly perked up, becoming a lot braver. Chester still scares very easily though... And while Henry always seemed a little more dominant than Chester, he's never been aggressive like this. In the past few days, Henry has been much more vocal, and my dad says they've been chasing each other around quite a bit. I've had a look through some old posts, and on the Finch Info site, and while I've got some basic ideas as to what might be causing this and what I can do about it, I'm not quite sure where to start.
All of their perches are at the same height, and there isn't any nesting material available to them. The cage is roughly 2 feet in width and height (a little bit taller than it is wide), and maybe a foot and a half in depth. The only thing I can think of that's different today compared to yesterday is that I moved their cuttlebone up higher, as they NEVER use it (I move it each time I clean the cage, hoping that one day they might take interest in it. (Actually, it looks like one of them has finally figured out what to do with the thing, as there's some obvious wear on it now. FINALLY.)) I'm going to try to pick up a bird pacifier tomorrow, but so far, I've found practically every toy I give them does nothing but scare them half to death

I've got a spare cage I could put one of them in if I need to, but I've got no idea how I would manage to get just one of them into it. Whenever I need to move them from cage to cage, I just open the doors, put them next to each other, and place a blanket or towel over the cage I don't want them in anymore, making sure that it covers the space above the doors so they can't escape. I figure I'm going to have to physically grab one of them, but every time I've tried that in the past, I've been unsuccessful. Does anyone have any tips for catching a finch?
Sorry that this got so long, I just want to make sure I'm explaining everything the best that I can. If anyone has any ideas or suggestions, I'd greatly appreciate it.
Thanks
