Hey, hope it's ok to jump in. Cool idea!

From a roleplay angle, what about adding psychological symptoms? Body and mind are always connected.

The curse seems to have a death-theme. You could have flare ups with temporary breaks from reality, visions, fever dreams (that may be true or not) themed around death that leave him both physically and mentally exhausted and weakened.

And partial or full transformation to a creature that is associated with death or is connected to the person or creature who placed the curse on the family, to connect it back to the origin.