What is the ruling on repeating the washing of the parts of ablution, and what is the ruling on the prayer of a traveler on an airplane if the travel duration exceeds seven hours, and according to which time zone should it be performed, and is it permissible to pray while seated on the chair?

The solution to what you are experiencing with ablution is to ignore doubt and suffice with two washes. Do not wash a third time if you doubt whether you have washed twice or thrice, because the third wash is a recommended sunnah, and so is the second, while the first wash is obligatory. It has been authentically narrated from the Prophet (peace and blessings be upon him) that he performed ablution by washing each part once, twice, and thrice. Scholars have mentioned that this was to show permissibility, and that three washes are completeness, while one wash is sufficient.

As for prayer on an airplane, the traveler prays according to the prayer time in the location they are in. They are permitted to combine Dhuhr and Asr, and Maghrib and Isha, either by performing them early (jama' taqdeem) or delaying them (jama' ta'kheer). If it is possible for them to find a place to pray standing, then standing is obligatory. Otherwise, they pray standing in their seat, gesturing for bowing and prostration. If that is not possible, they pray sitting.