Just a guess...

The suit being what's killing them is my guess as well. Honestly, after seeing other people walk outside, clean, and then collapse in minutes, why would they even bother with the suit? The whole point of them leaving is because they don't trust those running the Silo. Seems weird to accept their radiation suit that doesn't seem to work anyway.

Yeah, seems plausible and most likely ...

It is set up one way in the books, but there is no guarantee that the series is going to be the same. They have diverged from the book so far in several ways. I read the book so long ago now I am not even sure.

In the book, Holston's, "cleaning" comes pretty quick, as it does in the serious, and if I recall right he feels like he is choking, and realized the suit is out of air so he tries to pull his helmet off and has to break it or it finally comes off and he chokes on the poison air.

The problem with all of this helmet high-tech is that you can create virtual reality perhaps to match the real world, but you still have to present two different views to each eye of a person or the effect doesn't work.

I don't see how they can do that, or viewing the person's face from the outside of the suit, how do they account for all the different views people would have to see not to think something is wrong?

I don't know, maybe they will explain this somehow in the series.