Connecting one circuit to another via a transistor as a switch
The low current shouldn't be an issue (though that 2.6 Megaohm resistor may be, you want to saturate the transistor base, use a standard 4.7k of your ICE is low.). But not connecting the grounds would be.

If you don't want to connect the grounds, then use optocouplers instead. Avoids the ground issue and provides optical isolation.