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

No — not a sin in itself if there is no lust, no improper intention, and no violation of modesty.

Strict Jain answer: For the highest level of restraint, it is better to avoid changing clothes together in the same private room, because Jain dharma values lajja, maryada, and brahmacharya. Even if it is not a sin by itself, carelessness in modesty should be avoided.

In one line:

• Sin? No, not inherently.
• Strictest Jain conduct? Avoid it.