Sorry to hear about the folks, mine also went close together with Dad passing 9/03 and Mom in 6/04, they lived up near Auburn.
A quick search shows that your Dad's truck with that low mileage is worth $40-50K, depending on body type and trim level.
Parking it inside was a good call because you stopped any more water from getting in. The bad news is that it wasn't completely dry, and as soon as the weather warmed up you got some mold. The mold is also indicative of very high humidity levels which may be affecting the body control module (BCM) or similar computers that control the functions that showed codes. The instrument cluster may be junk or it may just not be receiving any signals from wherever it gets signals from.
As T&P points out, it's all very fixable. It may cost you $5k for the diagnosis, repair and de-molding, but totally worth it based on the value of the truck. Even if you don't want to keep it, get it fixed and sell it.