I actually wanted to thank you for posting this topic because when I read it yesterday, it sent me down some interesting avenues with the plugin and Twitter API in general.
Apologies that I haven't posted on this topic yet. I'm currently working on a couple of extra functions for developers to add to the plugin wanting to do to stuff like this in their own themes or plugins utilizing Tweeple, and I was going to put an example up in the Wiki I'm working on.
In essence, what you're asking exactly is not possible with Twitter API, in general. When we pull user's timeline, it's a specific resource from the Twitter API, that only allows one screen name.
You could do it with a search, but you're not going to get the result you want exactly.
If you were to search:
user1 OR user2
You will get tweets that contain either of those usernames in the text.
Now, technically you're supposed to be able to do a search like this:
from:user1 OR from:user2
Which you would think would return what you want, but it doesn't work consistently because you're tapping into a whole other resource of Twitter API:
And so you sort of get into the mess I was was talking about here:
As Tweeple rolls along, I'd like it to be possible setup your own display of Tweets with basic development knowledge. And I'm hoping to have an example in the Wiki of what you're asking, essentially where you'd take two Twitter feeds and just display them merged together, still keeping everything in chronological order.