Most people keep blue, black and splash birds together and call their pen BBS. It is very common practice and will not hurt to do this if you want to keep them all together in the future.
Here is an explanation of each possible cross and the expected offspring. It does not matter which bird is the hen or roo, it will turn out the same. You may want to save this info for future reference. Im sure you could also search for BBS breeding charts as well if you want more of a picture to look at.
Black x black = 100% black
Black x blue = 50% black 50% blue
Blue x blue = 25% black 50% blue and 25% splash
Blue x splash = 50% blue 50% splash
Splash x splash = 100% splash
Black x splash = 100% blue
As for your chicks, if you can get some pictures of them in good lighting, we may be able to ID them as being blue or black. Some blues are darker and hard to tell for sure but a lot of the time you can tell from hatch.