how big are they Ewan?
morphosed axolotls would be much larger than alpine salamanders. plumper individuals may well be females. mature males would have larger swollen cloacae than females(vent area)
heres a link to some pictures of the alpine salamander
http://www.herp.it/SpeciesPages/SalamAtra.htm
looking at some pics of the Santa Cruz Black Salamander, they appear to be more long bodied than your girls.
