Can a person's books, whether religious or legal, be dedicated as a Sadaqah Jariyah (ongoing charity) for his deceased mother, under the concept of "knowledge from which benefit is derived"? And how can Umrah be performed on behalf of both the deceased mother and maternal uncle during the same trip, taking into consideration the Miqat for someone from Qatar?

What you have done by printing the Quran and some jurisprudential books with the intention of earning reward will reach them in benefit and recompense. The same applies to donating religious books you own. As for legal books, it is permissible to donate them to those who can make good use of what is beneficial in them and beware of what is false. Performing Umrah (definition) for your mother and maternal uncle is a good and valid act, as long as you have already performed Umrah for yourself.