After discovering that his mother is dying, an exiled gangster turned priest must reconcile with the family he abandoned; but when his vengeful ex partner in crime threatens their lives, he must choose between his faith and his family.
A rewrite, just for the sake of tightening (and fixing the fact that it seems to have 2 inciting incidents):
After discovering his mother is dying, an exiled gangster turned priest must confront his vengeful ex partner in crime, in order to return and see her.
In case the final “her” confuses the reader (since “her” can be the ex partner in crime), you can also say:
After discovering his mother is dying, an exiled gangster turned priest must confront his vengeful ex partner in crime, in order to return and see his family.
People on this forum have mentioned several times (and rightly so) that “choosing between A and B” or “deciding something” cannot be the logline’s ACTION.
Choosing or deciding, first of all, is an internal process. Find the externalised manifestation of it and call it ACTION.
Second, choosing/deciding is a momentary action. So, he chooses A. The end. Unless complications arise. Then, we need to know how he deals with the complications. That, then, is the action, not “choosing.”
But your logline is definitely in better shape now.