Is it considered a sin to delay my Maghrib and Isha prayers until I return home due to being unable to renew my ablution after it was invalidated, and is this action forbidden, knowing that I feel regret, repentance, and seek forgiveness?

Praise be to Allah, who has blessed you with repentance and regret for delaying the prayer. The matter of prayer is grave, and delaying it beyond its time without a valid excuse is a form of neglecting it. Applying makeup is not an excuse to delay the prayer beyond its time. Repentance erases what came before it, and one who repents from a sin is like one who has no sin. It would have been better for you to begin with the Maghrib prayer before the Isha prayer, as observing the proper sequence between prayers is obligatory according to the majority of scholars.