Is it permissible to work in the sewing of masks and earn a living from it after verifying their authenticity through testing, and does the high price of original masks justify selling these masks at an affordable price to the poor?

If your aunt sells face masks claiming they are authentic when they are not, this is a forbidden deception (ghish muharram). You must forbid her from doing it, and it is not permissible for you to participate in it or assist in it. However, if there is no deception or falsehood, there is no harm in this work or in earning from it.