@Bob Smith
There are a lot of pieces missing from your story. First, consider none of us know your market. The first time you consider a rental, fear is a major factor. It is important to get another set of eyes to look at the property, and evaluate it. Look for another investor in your area, show him/her the unit, and get their feedback...what do they see that needs repair.
Talk to the local government. Surely, a rental license is required. Has there been one? If yes, ask the municipal government what repairs they are requiring. You might be surprised (hi or low) at the cost.
Next, go to a site that helps determine market rent. Your mothers case is an important lesson for any investor. Keep rents low at your own peril. You need to raise rents to market, so you can maintain your property.
Finally, consider the intangibles. The property has been in your family for years. Are you sure you want to sell it?
Also, if you think repair will work, try to acquire the property from your mother. If you get it, renovate the side she lived in and then moved out of. When that side is renovated, offer the unit at market rent to the other tenant. If they pass, tell them you have to renovate their unit, and give them notice. Renovate both sides, and collect market rents, and off you go.