My BIL1, actually it was primarily his Bovine Bride, were the masters at this.  Someone in the IL clan was always in their shit-bird seat.   No one ever would say anything directly to the shit-bird of the moment but it was open season on them behind their backs. BIL1 and the Bovine Bride would even attempt to get the shit-birds spouse to pile on.  SIL would pile on, MIL and FIL would even play along tacitly by not shutting it down.  Then Rags would show up and turn the spotlight on it all.

BIL2 never played along as he or his GF who became his wife were often in the seat.  As were DW and me, and even SS periodically.

DW would get so upset. This went on for years from when Bovine Bride branded BIL1 as her BF while he was in the Army and she basically kinapped MIL, FIL, and SIL and gave them all no choice but to accept her.  BIL went home for a short leave, and came back engaged to someone he claims he did not even remember from HS.  

After years of DW getting butt hurt about it, I told DW that if she was not going to say something to them that I did not want to hear about it any more or I would deal with it and no one would like it if I had to deal with it. She gave me a look, picked up her cell phone and called BIL1 and the Bovine Bride to ask them what their problem was.  A half an hour raging telephone fight resulted. That was the start of the devestation of the Bovine Bride and her bullshit.  14 years later she is all anxiety riddled, trolls for sympathy anywhere she can get it, and positions herself as the poor downtrodden family victim.

Interestingly, FIL would get blisteringly pissed off at the person calling it all out as the whole family is far more comfortable with the facade of blissful family happiness than dealing with the troublemakers.  FILs odd position on it all was heart breaking to my DW as it was DW who first communicated awareness of it.

That occurred when the IL clan had all (MIL, FIL, BIL1, the then Bovine GF, BIL2, and SIL) flown to visit us and to attende DW's swearing in as a CPA.  We were all heading out for a planned BBQ trail run when the Bovine GF announced that she had a migrane and that she and BIL1 were not going as she had to be in a dark room, etc.. to deal with her migrane. The rest of us left.  DW forgot her purse so we turned back so she could get it. She went into the house and overheard the Bovine GF laughing and talking about what they were going to do while everyone else was gone. We had left them the keys to our second car just in case.  DW was pissed and hurt. Instead of jerking a knot in their tails immediately, DW came out to the car with her purse, announced to everyone that the Bovine GF was faking a migrane.  Apparently DW's comment upset MIL. That evening after we got back from a inducing a meat coma on the Hill Country BBQ Trail FIL took DW aside and chewed her out and told her to never to that again.

This was a repeat thing with FIL when the shit-bird seat crap was highlighted.  No issue expressed regarding those doing the behind the back stabbing bullshit. Just anger at the person who would highlight it and call it out.

After the DW/BIL1/Bovine Bride telephone rager and start of the zero tolerance for the shit-bird seat behind the back stabbing era FIL did try to shut the spotlight and zero tolerance down.  Nope, I had a talk with him that he needed to focus on the problem and not the person/people trying to address the problem and his expression of anger towards my DW had to stop. That was the only tense discussion my FIL and I ever had after he and I stepped outside when I first met the IL family when DW and I were dating and he made it clear that I was to never touch her in anger.  I respected that. Though he did tell everyone else he had put me against the wall when he gave that message. That... never happened.  When it comes up in family gatherings I do not let the bullshit wall part of it slide. No one likes that but... for some reason, they insist on recounting how FIL put me against the wall.

After that it was BIL1 and Bovine Bride who called a family meeting because they felt like everyone was against them.  To keep it focused on improvement and future related I took the position of facilitator, set the agenda, set the rules, and I enforced them.  I was overseas when the meeting happened. DW was there along with the rest of the IL clan and BIL2's future wife.  I had to shut BIL1 and the Bovine Bride down several times when they tried to usurp the meeting.  They did not like that at all but when I told them to either follow the rules and agenda or leave, after a scowling pouting silence from them while everyone else kept working it all out they got on board.   

The shit-bird seat is now mostly a thing of the past though it does occassionally get dragged in from the crap pile and someone will try to resurrect the process.  It is actually funny how twitchy they all get when they think we are aware of the background crap.