Is every sin forgivable including the 5 mahapaaps no or yes strictest answer possible
No.
In Jain Dharma, sins are not “forgiven” by someone else. Karma must be destroyed by one’s own sincere repentance, pratikraman, restraint, penance, and purification.
Even the 5 mahāpāp are very grave. They can be atone for and purified, but only through true inner repentance and disciplined conduct — not by simple pardon.