One of my favorites! Here is a link to the species information on them:
http://www.finchinfo.com/birds/finches/ ... axbill.php
They are delightful, colorful little birds, with a pretty song (both males and females can sing). They are passive, getting along well with other passive species. Your two Zebras would probably pick on a lone bird, or even a pair--too pushy to share a cage. Males cannot be kept with other males if any females are present, but I now have 7 males together with no females with no problems.
They aren't as easy to breed, they need lots of privacy supplied with some plastic plants in their cage. Mine use the hooded wicker nests, lining them with coco fiber and white feathers. Unless you can get them to accept eggfood as their main source of protein, you will have to provide live mealworms to get them to raise babies. I have two pairs sitting now, so I'll see if they toss. Red-cheeked have a habit of scolding me with a loud chattering voice when I approach their cage while they have eggs or babies--my Blue-capped don't do this.
You will love the RCCBs!