Is 3 months old enough to not get chilled?

Over the past 2 months, I've been putting food out for the cat family in my backyard. A mama and two babies (there were four-- I took one because when I found her outside she was scared, dirty, hungry, and very skinny. She was alone and I thought she had been abandoned. The other I saw only once when she was with her two other siblings, my baby not included). Mama cat's name is Missy, her calico baby is Moonchild, and her dilute tortoiseshell baby is Flash. Flash is the most friendly one-- I can't touch him, but he'll let me get close to him. Moonchild sees me and runs. I've been wanting to TNR the mama (or socialize and adopt her out if possible) and rescue the babies so I can socialize them and get them adopted. I don't want them growing up feral, I want them in loving homes.

Anyway, this morning when I went out to feed them, Flash was hanging around and meowing at me. He never does this, so I kept asking him what was wrong. Well, he's a cat, so he didn't really give me an answer. Fast forward to later today, and it's POURING rain outside as well as thundering. I actually went out during to look for Flash at least (usually the only one who I see daily) in his usual spot, but I couldn't find him. It was cold out. What I'm afraid of is him (and Moonchild, and even Missy) stuck out there and getting too cold and dying.

It seems to be calm now, so I'm gonna head out again and see if I can find any of them.

In Summary: Concerned about 3 month old feral kittens stuck in thunderstorm, don't want them to get chilled and die. Are they likely to survive this?

Hopefully they found a place where they could stay dry.  Cats including 3 month old kittens can withstand chilly weather if they can stay dry.  You could put out some type  of shelter for them.  I saw Jackson Galaxy make shelters for ferals with large plastic totes.  He cut an opening for them and lined them with styrofoam cut to size.  He then put them up on 2 by 4s so they weren't sitting on the ground.

If they are 3 months old now is the time to trap and bring the kittens in for socialization.  They don't need their mother anymore and they are still receptive to becoming pets rather than feral.

I'm hoping they found somewhere dry to stay. They usually hang out under the hot tub (it's old and the bottom is almost completely torn out at this point, but they all seem to like it under there so I put their food just outside of it), but it looked like it got pretty wet when I checked. They like to hang out under one of the old cars, too, but it looks like that got wet as well. The porch is the only place I can think of that stayed dry, but I didn't see him or any others there.

I have a carrier they can go in (that I put food and water in as well) that has a blanket in it. It didn't seem to get too wet, but I'm definitely going to make them a shelter like that.

Yeah, I'm trying to trap them now so I can bring them inside and socialize them, as well as take them to the vet and make sure they're all healthy.