Joffrey’s thing was sadism. Oberyn’s thing is shagging everything he likes, and occasionally killing or hurting people, but that’s a side-interest.
Oberyn stabbed some guy because he was singing the song of an opposing house. He was then persuaded to let the guy go. Joffrey would have had everyone in the whorehouse, plus their babies, slowly killed. They’re not the same kind of person in the slightest.
Joffrey’s kind of “debauchery” will be filled in by Ramsay Snow.
Uncle/cousin, not brother, but yes, it would be reasonable for everyone to look uneasy without any ulterior motive.
Loris left quickly. That could just be because his ex-lover was being lampooned, and it would be understandable. However, if he knew that Sansa was being set up that would add an extra reason for him leaving - Sansa was very happy to marry him and he her, and it would probably have worked out quite well for both of them. From that one conversation he had with Sansa he would have known that she really is an ingenue who doesn’t deserve to be blamed for this.
Knowing that his Grandmother (and possibly his sister, though I suspect she’s in the dark - we don’t get previews at the end of the show in the UK) has set up Sansa could have given him extra impetus to leave.
This seems about right to me. Tywin sees Tyrion as a stain on the Lannister name, and as a defective monster who killed his wife in childbirth. To Tywin, these are unforgivable sins.
Tyrion never had a chance to be on Tywin’s ‘good side’ and was rejected from birth. That in turn made him cynical and turned him to drinking and whoring, which simply confirmed to Tywin that Tyrion was a degenerate.
However, Tywin came to recognize that Tyrion was also very smart and very capable, and therefore had no qualms about using him wherever he needed to. He made him Hand because he needed someone to do it and knew Tyrion was capable of it. He made him master of coin because he knew Tyrion was capable of it.
But none of that is going to make Tywin love him or even respect him. He hates Tyrion because every time he looks at him he sees a defect in the Lannister line, and he sees his dead wife. Tywin Lannister is perfectly capable of despising Tyrion while still using him wherever it makes sense to do so. He’s also capable of tossing Tyrion aside or even killing him with no qualms whatsoever. He’d probably enjoy it.