1- If we were travelling, after maghrib prayer can we wait until isha time to perform qasr isha? Or during jamat and qasr we need to perform maghrib and isha together without delaying the time in between maghrib and isha?
2-During zohor and asar time we want to perform jamat and qasr. If let say after zohor we go to eat and wait the time of asar we perform qasr asar. Can we do like that or after zohor we need to continue to perform qasr asar?

It is up to you. However, praying maghrib with jama'ah, and waiting for isha is better