Ok, tried the Shark after some time and everything worked for me.
Step by step:
1 Verify "easy communication" in the Options menu is turned off (not ticked)
2 Quickly created a mission with 2 Ka-50's, me in the first one, second one wingman set to AI. Left the comms frequency at default 124 MHz AM.
3 Started it up, turned on all the radios, verified AM/FM switch in the AM position, tuned 124.000 using the wheels, verified radio selection knob was turned to VHF(2).
4 Took off, wingman messaged me that he was rejoining formation, gave a few orders using the RAlt (plus) \ comms menu (change formation, hold position, rejoin etc.), wingman always responded and obeyed.
If this doesn't help, try repairing your DCS World installation.