Is it obligatory to postpone my Maghrib and Isha prayers until reaching my home country, or should they be combined with Asr during travel, or what must be done?

It is not permissible to combine two prayers before the time of the first prayer begins. If you will reach your country before Fajr, you may delay Maghrib and combine it with Isha as a delayed combination (jam' ta'khir). You would then pray Isha as four rak'ahs, as you will have become a resident (muqim). However, if you will not arrive until after Fajr has begun, you must pray Maghrib and Isha while traveling. If you are able to pray on the ground facing the Qiblah, then that is obligatory upon you. If you are unable, then pray according to your situation, even if on the airplane, and perform as many of the conditions and pillars as you are able, and what you are unable to do is waived for you.