you must have screwed up something with either your join command or the
join command simply doesn't get executed because of some other mistake.
You 'can' let east units join a west group/unit.
There's just another problem with it:
If you let's say let two east units join a west unit, they will join him
but open fire onto eachother because they still see eachother as
east units but know they themselves are now west.
That's weird, isn't it.
But there's a work around besides the one Myke has told you.
If you don't have resistance in your mission, let the two east guys
start as resistance by using the technique, myke mentioned and
set resistance to friendly to everyone.
Now place a resistance unit with a higher rank than the east guys
and group them to him. Set the resistance guy's condition of presence
to false so he will not appear but they will be resistance now.
The two russian soldiers will now fight for whatever side you make
them join no matter how often - from start they are resistance and
friendly to all which will make them not fire onto eachother whoever
they join.
I've attached an example mission, where you can let them join either
onto the player's group (radio alpha) or onto an east officer's group (radio bravo).
If you change the radio-triggers to repeated you can play around with them
and let them join vice versa.
Ah btw - the mission you will find on desert island name: east_join_west_example.
:edit - i corrected - probability of presence into condition of presence
~S~ CD