You have a 30 year old unit. You don't state how old the AC units are. IF original, then YES, it is better to replace BOTH Penguin's with the new style. The New Penguin's have on board 12 button control boards. Then after replacement, you just replace the wall tstat with a new 12 button Tstat. BUT, here is the problem. The Tstat and control systems for the current Control boards were not introduced until 1999. In 1999 Dometic went to a Communication cable system between the AC units and the wall tstats. This cable LOOKS like a 4 wire modular Phone cable but it wired in reverse of a phone cable, so you cannot use a standard phone cable. I need MORE info from you. You should have 2 wall tstats from your year model. Also, if the old style tstats, Dometic makes a adapter harness, to make the existing standard 6 wire tstat wire with a modular end. Also, IF 2 wall tstats, you will need 2 new 12 button wall tstats.
This link shows the adapter kit. You would need 2 kits.
https://www.amazon.com/Dometic-3106986007-Cable-Adapter-Kit/dp/B00T36PFB6This link shows the wall tstat.
https://pantherrvproducts.com/3314082-011/?gclid=Cj0KCQjwhL6pBhDjARIsAGx8D5_eZQDuxhPl9woPEfueN9VVVx3RZq3XG-UgPE_PeeicRECzlJVFzQ0aAu32EALw_wcBWHICH WALL TSTAT DO YOU HAVE? 4 BUTTON? 5 BUTTON? 10 BUTTON?