We can meet on the way there?

Meeting on the way there doesn't specify any point where you're going to meet. Meeting halfway does. That's the only difference I can think of. I'm not sure I'd call it an idiom.

1. Let's meet halfway.
Usually used when people in two different places (A and B) wish to meet; the suggestion is that they meet at a place half way between A and B, thus none have to travel the full distance between A and B. However more often used metaphorically to mean "In our dispute, let's make an equal compromise between our opposing requirements".

2. We can meet on the way there.
People are going from different places to a common destination; the suggestion is that they meet somewhere which is an intermediate point common to all of their routes.

3. Let's rendezvous and go together.
This means the same as (2.), with the emphasis on the intention that all shall arrive at the common destination together.