Thomas, Clearly there is a lot of history between MOM and the DAUGHTER, much of which predates step dad. Step dad didn't create the problem and isn't really in a position to fix it AND simultaneously get along with his wife/DAUGHTER'S MOTHER. He was put into a difficult position. This action, unfortunately, was allowed by MOM who is playing with a script well rehearsed before stepdad got involved.
The result this time is about as much as could be hoped for by step dad unless and until MOM grows a backbone.
Once you negotiate (or give in without negotiation) when dealing with terrorists (blackmailers) they can manipulate you over and over (past, present, and probably future of this group, irrespective of who the boyfriend of the week happens to be.)
Why are so few Russian citizens kidnapped for ransom in foreign countries? Generally the Russians did not negotiate so the terrorists gained nothing but victims which could have been just as unprofitably randomly selected off the street. Then in the background the Russians moved heaven and earth to wreak havoc on anyone associated by at least a factor of 10 compared to their losses making it a no win situation for the terrorists. If you know going in that your threat will not gain you anything, there is no incentive to take the action. If you strongly suspect from past observations that it will cost you dearly to try, you are less likely to try.
To break the cycle of intimidation requires exercising adult judgment and free will (re my grow a backbone comment) which in a situation as described is difficult as the daughter has conditioned mom as sure as Pavlov did his dog to get her own way. I'd bet she had mom well trained by an early age for the daughter. Daughter may have been one of those I'll make a scene if you don't give me what I want types, wiling to throw a fit and kick and scream till placated. So long as if you hold out long enough that MOM gives in, you reinforce the conditioned response for both the terrorist and the victim.
That'll be 5 cents please!
Pat