Inherited Omega Seamaster

Your watch is a "waffle dial" Omega Seamaster reference 2846, manufactured in the late 1950s. The serial number on the movement would allow a more accurate estimate of the production date, but it is covered by the rotor in your photo. This is known as a gold-capped case. It should have either a caliber 500 or 501 movement, but again the caliber number appears to be covered by the rotor.

Fortunately, I do not see an actual crack in the case-back, since that could not be repaired.

The watch looks great. Personally, I would just have the rust cleaned up and the movement serviced, which may cost a few hundred currency units from a skilled independent watchmaker (this is an international forum, and I don't know where you are located). Please, go slowly with any restoration, since things like case polishing or dial cleaning cannot be un-done if you're not happy with the results.

https://www.omegawatches.com/en-us/watch-omega-seamaster-omega-ko-2846

Just a quick note. Looking more closely, I am seeing some "rotor rub" in the movement, and obviously some pitting from water intrusion on the back of the case (and a little bit in the movement itself), so there may be some corrosion in the movement that needs to be addressed. This can all be repaired by a good watchmaker, and I would not hesitate to do it. This is a nice watch, and obviously it's a family piece. However, the watchmaker may need to replace some parts, so the service cost could be a bit more. Honestly, it is hard to know until the movement is completely disassembled. But don't panic, it will be worth it for your heirloom, and once repaired, it will be something that can be passed down through the generations. It will be good to find a watchmaker who is experienced with vintage watches.