Brandon is still pretty hardcore IBLP, but the guy clearly loves Michaela a lot. He takes one for the team a lot with putting up with her family. Unlike the other sisters' husbands, he's not the construction, plumbing, electrician, HVAC type. Instead, he's more artistic and almost cerebral from a fundy.
Kelly Jo is pretty notorious about making her daughters do things others would find uncomfortable. In the first episode of the series, she hosted a baby shower for Whitney. Erin, who had been due around the same time, was called in to not only help with invites but plan, shop for, and host the baby shower games. Now she's hosting a shower for Carlin and wanting Michaela to do the food because all the other older girls are at home preparing for a babies or just had their own babies.
I know these girls seem to let it roll off their backs, but that woman is incredibly insensitive.
You are right that they aren't able to socialize outside their little circle. I remember watching one of the episodes where they were talking about Josie and Kelton talking. They said primarily they just talked about family and Bible verses. I guess it makes sense. What else do they know enough about to make conversation? I am guessing they watch television at some point and even some movies (based on things said and the presence of such items in their homes), but still they are pretty stunted.
I can understand Carlin wanting to have attention in a family that large. It's natural. Heck, I'm an only child and I was annoying as crap when I was growing up because I never wanted to do my school work. I just wanted to talk to my teachers. I didn't even like the other kids most of the time because I was always around adults and thought kids were kind of dumb. There is just something about Carlin's over the top nature that is so fake to me. I never find her genuine at all. Michaela, Alyssa, Tori, Josie, Katie, etc. all have moments where they are not putting on an act and seem real - whether that is real annoyance over the clutter or noise or real affection. Erin and Carlin just seem to have a facade that screams out fake.