Hi Joe, please see this post by Bryan using both Javad’s Justin 3 and CHC Geomatics Office 2 PP software for post processing. I believe they are both capable of using multiple baselines for processing.
More information on Javad Justin 3 here
https://www.javad.com/jgnss/products/software/justin3.html
And CHC Geomatics Office 2 PP software is available here:
https://iggps.com/cgo2/index.htm