If he's blackmailing you, find a convenient way to drop in on him or get invited into his sanctum, steal an Arcane Connection and send it to the Lineage of Pralix for them to fix. They can then leisurely hand it to non-hermetic magi to cast spells with at sunrise or sunset while the Tremere is busy performing parma magica. After all, technically there's nothing in the Code about using non-Hermetic magi to do your dirty work for you...
Or you could just write to members of the lineage of Pralix, point out that he is blackmailing you, and see what they are willing to do.
Another fun thing you can do - instead of teaching the virtue (using the rules from the main book and requiring a huge Com + teaching), say you will instruct the apprentice - and then experiment on them like crazy while you do it. Maybe you can ask if you can experiment with their gift (like in the bit in Hedge Magic:revised edition for Folk Witch "gentle opening"), or insist on creating an experimental Mystery Initiation script and using the apprentice as a guinea pig - maybe they'll get lucky and get an extra bonus, or maybe they'll get extra flaws for their trouble.
lineage of pralix is not a misrery cult. Its a lineage. They are powerfull and well conected teachers in thr ex miscelanea house. They are an ancient lineage with a lot of history and the only reason for being so small lineage is because they dont teach so many aprentice but teach others traditions. So they are skilled teachers and have contacts inside and out of the order. His magic resistance is flawed because his powerfull skill and i can conceive the comprehend magic without thenflaw and without the focus, it seams as obvious sinergy of comprehend magic and hermetic magic. So, i see them as powerfull magi devoed to the order, prestiged teachers inside the house and maybe in the order as well with a mission of strent the order, protect the minor traditions or bizarre secret plot to rule them all, but never as inocent loners. They are tytalus, in the final case xd. As users of a strange skills they must make a net to exchnge tractatus and improuve comprehend magic.
This about the pralicians.
About your trouble, Sauryan, this is not about rules or backgrund interpretation, this is a psicological problem of your alpha storyguide. If you want to keep playing with this guys just talk with the toupe. And try to guide a story sometimes.
When in game be as tricky as posible: say with your mentor and tell him about the tremere axxhole, dont care about consecuences, its just a game. In your sanctum you can kill even the aprentice of your alpha storyguide wih no legal consecuences. and no one can, with the code, to force you to teach the magical secret. Indeed this is not a research of your magus but ancient secret of the pralicians. Feel you insulted and just dont be polite with the tremere. You can also take the aprentice, take the vis and dont teach nothing, as jason and jhon said. Also you can leave the alliance and go Durenmar to study for 15 years.
Thanks guys for all those info, il will base my rp depending of what he does ! ^^