All depends on why they are not closing and the condition of the existing frames. Are they installed plumb, level and square? Are the doors warped?

Installing prehung interior doors is usually much more inexpensive than fitting new slabs to old frames.

In your case, there has most probably been some settling, meaning all the door frames are out of plumb/square.

Installing new prehung doors is the better solution.

You don't necessarily need to have the door frames replaced. My 1950 home had all maple door frames and trim - the doors were butt ugly.

I numbered all the doors, purchased new 6 panel doors, had a shop mortise hinges and bore door latches same as the old ones.

If the frames are a little out of square, the doors can be planed.

The top hinge screws could be loose, allowing the door to "hang out" a bit further than it should.

Close the doors and look at the reveal on the three sides, plus the floor. If the door can't be closed, see what part of the door is catching on the jamb.

Several doors being out of whack the same way can indicate simple setting of the house.

With the door closed, if the reveal between the bottom of the door and the floor is uneven, that can indicate house settling too.

If stain grade, it might be easier to just replace the doors. Matching stain color and wood grain can be an issue if that is a concern.

If paint grade, as has been mentioned it would be easier and probably less expensive to replace the doors and jambs with prehung units.