A tank that is warm enough for the frogs will be much too hot for newts or salamanders. You also run a huge risk with mixing toxins from different species.

I would NOT add any salamanders (all newts are salamanders) or you run the risk of killing them with heat.
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1.1.2 Python regius
0.0.1 Eunectes notaeus
0.0.1 Lampropeltis spp.
5.0.0 Ambystoma mexicanum
1.3.0 Triturus karelinii
1.3.0 Taricha granulosa
0.3.0 Ambystoma jeffersonianum
0.0.3 Salamandra salamandra
0.0.1 Tylototriton verrucosus
1.0.0 Grammastola cala
1.0.0 Homo sapiens 'Hottie'