Just watched the highlights.
No idea what Telfer was doing. They were probably told to 'target' Hendry and he's taken it too literally. Having said that, it wasn't a 'studs up, flying in' type of tackle and he, like everyone else, probably thought he would get off with a yellow. I think Hendry's reaction helped make the Ref's mind up TBH.
Gomis's first yellow was unwarranted IMO. Both players going for the ball and collided with one another. If you freeze the footage just before however, you can see Armstrong going in with his studs up and catching Gomis on the leg. If anything, the booking should have been the other way around. Regarding his second yellow, at the time I thought the Raith forward was further up the pitch and that he had no option but to pull him back however there were two defenders there that may have been able to do something so he could maybe have avoided that one.
The Raith guy's second booking for the sending off was certainly merited however, I can't remember what his first was for (unless it was he that elbowed McManus in which case he shouldn't have been around to be booked twice) so don't know if he deserved to walk or not?