My siblings are agnostic, should I try discussing atheism with them?

[robvalue]

I'd say it's fine to talk about your own beliefs (or lack of), as long as they are comfortable discussing them. I would recommend against trying to convince them to change their position, that thing never tends to work if it hasn't partly come from them. You could always let them know you're there for them, if they want to discuss these things.

If they "aren't sure", then they are atheists, by definition. Whether or not they are comfortable with that label is another matter. People who say they are "just agnostic" are atheists, by the common correct usage. But trying to make people use labels they aren't happy with is rather pointless.

My website might help clear things up further, and I did a video about recently, if they are any help to you or your siblings.

https://www.youtube.com/watch?v=d34BmGnrUEI