Honestly, I think Rick made the right call when it came to refusing to let Merle back into the group. Five minutes into the rendezvous in the woods and Merle was already stirring up trouble and picking fights with everyone in sight. Let's not forget, there was a reason Rick had to handcuff him to that rooftop in the first place . . . .
And regarding Tyrese's group . . . well, at least two of the newcomers were already
plotting to seize control of the prison, so Rick's not entirely wrong in suspecting that these strangers could pose a danger to Carl and the others.