To my mind , Rick is reasserting his authority. What carol did was probably the right thing to do, but done without his permission; same as she did teaching the children how to kill zombies.
Is it Ricks place to expel a member from the group? Well if he was still the recognised leader, yes; but at the moment he isn't. What he is doing is saving the group a dificult decision, and probably saving her life from the vengeful Tyresse. Perhaps he is also wanting to keep Daryl with the group instead of going off with Carole; there's nothing to suggest that he will tell them the truth.
Interesting that Carole mentions not wanting to leave the children behind, but not her lover; still,she knows where the prison is and can go back for him. But I think that she's grown cold hearted enough to want to make it on her own.
As for the unlucky couple, another reminder of people who don't have groups or communities being bumped off, but a little too contrived for me. Just 2 zombies in open space, and her with a pistol? She's survived long enough, but within minutes of meeting Rick she's dead. And why would her severed leg be so far away from her body? Zombies don't have a habit of dragging bodies away. Seemed very contrived to me.
I can't understand why Daryl's group wouldn't have wanted to leave the same way that they had entered the building; they're getting quite used to surviving in zombie-packed buildings. Quite why they would be following the exit signs rather than backtracking to the (presumably safe) way they had entered the building I really do not know.
It was interesting to see the contrast between the two groups though. Firstly Daryl allowing two members to stay, onewho had put the group at risk on several occasions. Perhaps he doesn't feel that it's his place to make those kinds of decisions or perhaps he's too kind hearted. Personally I don't believe rock had any intention of bringing Carole back to the group; he just wanted to get her far enough away before telling her. He may have even made his mind up when he found out from his son abouther teaching the kids. He can see his son going down a similar cold-blooded path and maybe wants to send him a message; the thing is that Rick is just as ruthless as Carole, but he hides behind his group leader rather than admitting it