Peter, sorry to hear of your Dad's passing. You are a good son for trying to help out your Mom.
The good news is that your Dad's car is a 1975 and will not require the bi-annual smog check in California which makes it more desirable for Ca owners that want to do engine modifications. The 1975 "square-tail" wasn't the most collectable BMW 2002, but can fetch prices in the mid to high teens in top condition. Your Dad's car will require some work to get it close to those numbers.
First off, your car running and driving will significantly raise the price. @Mike Self had a great recommendation for trying to re-start that engine. I would buy a battery for it, test all the lights and electricals and try to start it. If it is damaged from running without oil, the lower end will probably knock badly and you can use that as a decision point for how to proceed. If the motor is good, I would clean up the interior, install the trim, get the hydraulics sorted (clutch and brakes) and see if runs and drives. This all assumes that you are doing the work yourself. If you aren't mechanically inclined and need someone else to do this work, you can get upside down in a hurry.
If the motor is toast, you will need to at a minimum pull the engine, install new main bearings and turn/polish the crank and inspect the previous work. I would budget $1.5K - $4K for this work, depending what the machine shop discovers. If you aren't prepared to go down that path, the car still has value, just not as much. If you just bolted on the trim, washed, waxed and buffed the paint, installed the door cards and detailed the interior and sold it with a motor that needed rebuilding, you could get $6K - $8K for it. As it sits right now in the pictures, you could probably get $4K - $5K for it.
IMHO,
Mark92131