Yeah, Cersei set up Robert, but didn't Jamie finish him off? Anyhow, I'm not sure if people found out about that anyway, but since they kept calling him kingslayer, I assumed they knew.
Man, tell me about Tywin. Cersei's first husband said another woman's name during sex, just imagine how sex would be if she marries Tyrell. Tyrion got the sweeter part of the deal really.
Remember that Jaime had already assaulted Ned, killed his guards and ran out of town when Cersei arranged Robert's "accident".
If Loras and Cersei got married and were expected to produce an heir that would be a very long and likely very uneventful wedding night.
Do you think that either Tyrion or Cersei could say no to their father as far as marrriages? I was wondering about that. It's one thing to have an arranged marriage when you're a kid but they're both well into their thirties. What would happen if they each refused Tywin's order?
"When the snows fall and the white winds blow, the lone wolf dies but the pack survives." Winter is Coming Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die. As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.
Tyrion got the sweeter part of the deal really. 
