Check out my build thread starting on page 4.
I've mounted the back seat out of a Chevy Tahoe, I think it was a 2014. Bought it on ebay from a guy in Texas. It may have been a sheriff vehicle take out.
We have two kids and wanted to put the bench seat back far enough to make a "living room" area combined with the front swivels. It worked great. We do have some fairly bad vibrations that come through the rear seat while driving. The seat belts have been a challenge.
I had very talented fabricator do the install and i've been quite happy with it.
Good luck. Those Sieanna seats look ideal.