Salaah on a Conveyance

Repeating the salaah performed on an aeroplane while seated

Q: I read in one of your fatwas that if a person is unable to pray standing in a plane and therefore prays seated, they must repeat the salah later on. Is this because 

* The first salah was invalid - so that they should intend qada when they repeat it? 

* Or was the first salah valid (i.e. fulfilled the fard) and the second one just a repetition of it in a more perfect manner?

Performing salaah while on the aeroplane

Q:

1. If I am travelling on an aeroplane, and the salaah time enters, then what is the correct way of performing salaah and what timing do I follow for each salaah?

2. If there is not enough space to perform salaah due to the aircraft being small, or the airline does not allow me to stand and perform salaah, will it suffice for me to sit in my seat and perform my fardh salaah?  

Performing fardh salaah in a car

Q: While travelling in a car, my family prayed the obligatory namaz sitting in the car. Later I found out that sitting while being able to stand invalidates namaz. It was also raining heavily so is the prayer valid as it was done out of ignorance or should I tell my family to repeat those prayers?

If they have to repeat it, should it be prayed as qasr?

Performing salaah on a bus

Q: I am an employee in india. The maghrib time in summer (which is the season right now) starts at/after the time when my office bus starts (6:30pm) to drop the employees. Since I take the office bus and my home is approximately 2hrs, my maghrib takes place in the bus whilst being seated. There is very little khushoo with everyone staring at me and it is troubling me a lot. Is it valid for me to join my maghrib prayer with asr so that I can pray it peacefully in office before starting? If valid, can I join asr and maghrib until the sunset time changes to before 6:30pm which might take 4-5 months?