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

[ErGingerbreadMandude]

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

Where's the ignostic one???? ;<

[Cyberman]

Why try to push a rolling stone?

It would get me satisfaction?

[robvalue]

Pool: Yeah, I need to add a about ignosticism to my website. I guess I thought it was overkill for people who are new to atheism in general.

[Minimalist]

Why try to push a rolling stone?

It would get me satisfaction?

I thought you couldn't get no?

[Cyberman]

But I try

And I try

And I try

And I try.

[maestroanth]

It's probably worth discussing with them.

You might want to approach it by first defining the terms "atheist" and "agnostic" with them.

If you explain the formal definition of the words, instead of the colloquial definitions, it might get them to accept that they are already atheists.

You could also show them this:

I've always get kind confused about the agnostic/atheist labels.  Like by definition, how can you 'believe' in something you 'don't know'.  If you don't know if say purple unicorns exists, how can you say you believe in them?

...... I guess that is what you're getting at when you mentioned the 'formal' definitions of the terms rather than the colloquial......

[robvalue]

I believe my car is still parked where I left, but I don't know that it is.

I'd say the difference is that if you know something, you should be able to demonstrate it (within reason) to be true. If you just believe it, you may think it is likely, but you can't necessarily produce evidence at that time.

I believed the answer to a puzzle was a certain number; my intuition was telling me it must be correct. But I didn't know it, and I wasn't satisfied until I had demonstrated to myself that it was indeed correct.

[LostLocke]

I believe my car is still parked where I left, but I don't know that it is.

That's a good example.
Another would be, I believe the sun will rise tomorrow.
While there's a crapload of evidence and indication that it will, and absolutely nothing that says it won't, I still technically don't know that it will. I can't know that until it's actually happened.