me and my mother change clothes together in a room private is it a sin no or yes strictest answer possible even if we were naked

Strictly speaking: yes, it is not proper in Jain Dharma for a householder.

In Jain discipline, intentional nudity or changing clothes naked in front of another person, even a parent, should be avoided. A Jain householder should follow modesty, restraint, and dignity in conduct.

So the strictest answer is:

• Yes, it is improper and should not be done.
• It is not the conduct of a Jain layperson.
• If it happens only out of necessity or by accident, the karmic fault is less than if done carelessly or deliberately.
• The safest Jain conduct is to change clothes privately with body covered.

If you want the answer in one line: Yes, avoid it.