Advice on preserving an old painting
You should consult a professional conservator.

If you're not even sure what kind of paint was used for this painting, chances are high anything you do'll cause more damage.

A conservator can see what kind of paint was used, what may have caused the damage (moisture, too much tension, deterioration of the paint?) and how to effectively stop the damage from spreading. Usually they would have a look at the painting and give you an estimate of the current value as well as an cost estimate for the preservation or repair before you have to decide whether or not you want to engage them.