This is how I think the relationships are:
Flashnose + Stagleap = Swiftbreeze & Stormtail
Idk where did Stormtail's color come from, but Swiftbreeze is described as tabby. We don't know if brown or gray, just tabby, so it can also be gray tabby. In german books, she is gray tabby, so I believe she is gray tabby, which would be genetically possible as Stagleap is gray tabby. And Vicky thinks Stormtail is Swiftbreeze's brother, so I think so as well.
Fallowsong + Littlestep = Poppydawn, Rabbitleap & Heronwing
Sweetbrair + Nettlebreeze = Pineheart/star
Mistpelt + Mumblefoot = Smallear & Rockfall
Smallear would have the amber eyes of Mumblefoot, and gray fur of Mistpelt.
...Does anyone have any idea how did Adderpaw/fang come to be? I can't come up with anything... I think he might be son of Mallowfur, but that's just a theory.