Connor and Isolde

Blood magic is obviously out of question here. I'd say either going to the mages or killing Connor is fine. The latter doesn't cost you any approval with Leliana if you allow Isolde to be the one to finish him off.

Then again, you said you already have left to get the mages so I'm not sure what choice you're talking about.

It all depends on your Warden's perspective. As far as companion approval goes, that can pretty much be negated (more or less) through conversation choices and gifts.

My two main wardens made different choices, but the choice each made made sense for her (remember, as players we known that we can go to the Circle with nothing bad happening, I don't feel that the characters did).:

Naliea Tabris: Redcliffe was the first stop after Lothering. While in Lothering she heard about the trouble at the Circle (as well as from Bodahn), so she knew it would probably take even long than expected to return from the Circle with help - if the Circle was even in a position to help. Even with all them fighting, they barely made it through the attack on the village, so Naliea was sure that whoever was left behind would end up dead. (Didn't trust Jowan or Teagan's ability to control Connor: a) they'd don't a bang up job of it so far, and knowing that they were going to find a way to defeat it, the demon would fight back enen stronger.) She wasn't very trusting at this point, what reason did she have to trust Jowan - especially seeing how big a part he had in creating this whole mess to start with. As much as she hated it, she felt that killing Connor was the only viable option. Although it the one decision she regrets having to make, she stands by her opinion that it was, regrettably, the only way.

Lora Cousland: Again, Redcliffe was the first place she went after Lothering, so not too long after losing her family - I think she was still in a state of shock/mourning/PTSD. The thought of killing Connor was even less of an option than it would have been - she can't help comparing him to her nephew. As far as Jowan's blood ritual went, as a devout Andrastian that option was out, especially when it would require not just someone's blood, but death. Even though it was a gamble, going to the Circle was the only option for her.

Note: I headcanon these two as dual wardens. Lora and Alistair make the decision to go to the Circle. However, Naliea takes matters into her own hands (for reason stated above) and kills Connor ( lets Isolde do it). When Lora sees Isolde holding Connor after it's done, all she can see is her mother cradling Oren's lifeless body. It definitely created a rift between the wardens during the early part of their adventures...

You evil bitch! Lol j/k.