given that frames are evil (
my point is somehow different.
what's the meaning of TWO web servers serving the same page?
we are not balancing load, doing something faster, lowering latency, nothing.
So why different servers?
if you need 2 different pi to do different things (temperature and flight-something-that-i-did-not-understand) that's ok, but if you need to serve informations to clients.. well, i'd look to a way to split DATA from REPRESENTATION
this would be a clearly better rolution.
But remaining in your question.. if both your pi will be accessible in the same domain by clients, you can try to build a good looking css page with divs and load content into divs with jquery load() method
given that (luckily) the same origin limit is quite rigorous ( https://en.wikipedia.org/wiki/Same-origin_policy
), i think this would require "something" (like a reverse proxy) in the middle.
Did i say that frames are evil?
Edit to add:
LOL i swear i was not referring to your nickname!
Edit again: reading the page i posted, interesting for you the "Relaxing the same-origin policy" section.
Try to get it to work using two different subdomains "pi1.you.com" and "pi2.you.com" setting the origin domain to you.com
should be interesting..
you need 2 different public ip for this (or again a reverse proxy), if you change port to reach pis it will still not work