As our children have settled abroad, we are compelled to travel overseas. When we return home, we atone by bathing in holy rivers and partake panchagavyam. While we do atonement many times, will such atonements remove our sins as we have transgressed against the ordain of scriptures? Why travelling overseas is wrong fundamentally? Please clarify.

As per Sastras, yes these atonement to some extent will purify us
Smritis say that one should not travel to overseas.
Obeying the ordains of Vedas are virtuous.
In those days there was a restriction for going abroad, because the connection of our Vedic tradition will be completely cut off.
Notes:
“paNNiya nal vratamellAm palikkumenRu
bhAradattai pangayattOn paDindittAnE”
Even the devas come down to Bharata, the karma bhumi, for acquiring merits. The good deeds rendered here alone will fetch good fruits. Hence travelling overseas is prohibited.