Is it possible to have two SIM transmitters but set on different channels working at the same time?
I think you mean ISS transmitters - all VP2 transmitters other than 6345 use the same circuit board and so are effectively SIM transmitters. But if you mean 2 transmitters each being received as an ISS at the console then the basic answer is no. (Solar/UV sensors can only be received as a transmitter configured as ISS type.)
There are always a couple of caveats to this question: One is that receiving solar data on a second SIM transmitter can be done with an Envoy8X console or a Meteobridge Pro Red unit, but neither of these is compatible with the software you're probably using at present. Mark Crossley has another solution that he might want to comment on, but again I believe it's not quite a drop-in fix for an existing data-flow.
Ah and one other caveat: It is of course possible to receive one SIM transmitter as an anemometer transmitter and have a second SIM transmitter as the ISS with T/H, rain and solar/UV attached.