This looks to be pretty normal to me, although when mine get poop stuck like this, they typically do clean it off. Your girls (especially the BR) have pretty fuzzy bottoms, so I can see how some poop would get stuck on those fuzzy feathers.
If these 2 have runny poop, though, it's cause for concern for your other 3. The two could have something that could be passed to the other 3, so you really should consider finding a place to quarantine in case you have an issue in the future, OR getting a few pet carriers (that's what I use) so they can be separated to treat them if this does end up being somethign they need to be separated for.
Enjoy your new girls!