H.orientalis is a very tough species that requires very little to be at optimal conditions and thrive. The problem of course are WC animals which are treated terribly.
The terrestrial animal is almost cerainly suffering a combination of the left over stress from importation and current inadequate conditions. They frequently go terrestrial as a result of the misstreatment and remain so unless water conditions are optimal. They are at their pickiest at this time, once they are aquatic they tolerate a large spectrum of conditions.
Make sure your water parametres are ideal and that your tank is very heavily planted. The newt needs perfect conditions to recover.
As for the mix, very bad idea...there are several reasons for this...pathogens, competition, hybridization...