Can you open and close the cracks by pulling the coaming? I wouldn't bother trying to restore this to some cosmetic original with a varnish finish as the wood is stained and the effort to get down past varnish and epoxy would be too much work.

Put kayak on side doing one half at a time. Mask deck under coaming 1" out from coaming stack. Wire brush and hand sand with 100grit. Paint with low viscosity epoxy to fill cracks. Follow with a fillet of thickened epoxy that turns the sharp right angles into curves. Once fillet is firm set follow with a couple layers of bias cut 4oz cloth that go from deck to underside of coaming.

Repeat on inside of coaming making sure to round over coaming stack.

The major problem with those kind of bent coaming constructions is that the un glassed edge grain of the soft okoume ply just isn't that durable for the abuse a sea kayak gets. The thin edge requires a lot of epoxy to withstand finishing sanding and even then it eventually gets whacked through resulting in water intrusion.