Pictures? What is crumbling? Mortar? Bricks? No spray nothing will hold it together.

Please post pictures

Kind of hard to tell without being there and getting a feel for stability of chimney. What is chimney like above the roof? I assume the liner is single wall and requires masonry around it. Fix might involve piecing in some new brick and mortar: it doesn't have to look pretty. I'd want to make sure that metal isn't exposed, especially as the chimney goes through the opening.

"Is there any other option short of hiring a mason to repoint it?"

Looks like some serious deterioration of the masonry--the full extent of which might not be known without some disassembly of the chimney. Another option available to you is removal of the masonry chimney altogether, but that will likely necessitate replacement of the flue liner with an approved metal vent. In either case, you'll need to pay particular attention to the flashing of the chimney or the new vent pipe at the roof.

The chimney on the roof is cinderblock and in fine condition. We had a new cap installed with the liner and then new flashing after the liner (previous owners did not have tbe chimney properly flashed!).

This old house has some videos on repointing brick. You could find them. You need to be super careful to get the right mortar, since the wrong one will make things worse.

We bit the bullet and had our chimney, which looked pretty similar repointed.

You're missing some brick near the top and the brick just under the roof line, in the upper quadrant has spalled, and should be replaced.

You need a mason to determine the proper repair. I think this will requie removing the exterior cement block and bricks to a point where there is a solid structure. It seems the brick is too damaged for a patch repair.