newbie help plse

I believe the 3gxmr/t6 uses the futaba protocol. I'm not sure which one, but we don't currently support any futaba protocols with Deviation, so I think that one is going to be hard unless you change the receiver.
The trex250 should work fine on Deviation as it is DSM2/X
I think the V911 ver2 still uses the Flysky protocol, so that one needs an A7105 module
The v931 uses the KN protocol which requires an nrf24L01 module

So you can get 3 of your 4 models flying with the same transmitter using Deviation and 2 add-on modules (which you need to solder into the transmitter)
You could use any supported Walkera transmitter, but I would recommend a Devo 8, 10, or 12. The 7e could work, but requires an additional mod to get full range, as it is really intended for micros. The F7, F12, and F12E are not yet supported by Deviation (The F7 is getting close, but due to its limited hardware, I wouldn't recommend purchasing one)

yes, usually the modules can be pulled out of the existing transmitters with a little soldering skill. I don't know the specifics of these transmitters, but if you want to be 100% sure, you could open them and take a picture. Usually the RF module is easily identifiable.

One note, I think there have been some issues regarding the BeastX and Deviation. I am not sure what they are and whether they are user-error or real issues. I recommend searching the forum 1st.