How and why are two lines of cloud formed by airoplanes. What type of airoplane engines cause this(is it is caused only by war planes or do commercial planes too emit this parallel clouds?

It's called a con. (condensation)trail. It's from hot exhaust gasses from the engine hitting the cold, High altitude air forming tiny water droplets.

I live directly in line with a the main runway at an International airport and about 8 Km from it. We see a yellow substance on our cars and laundry. Could this be from pollution of the aircraft?

Possibly, but they've cleaned up particulate matter from jet engines quite a bit over the past years. Also 8 km is a good way out and one would not think that any jet emissions would be so concentrated at that distance (i.e. the planes would be at such an altitude) as to leave noticeable residue. There are other possible sources, or a combination of sources - including cars, trains , industrial activities, and even plants (e.g. certain trees at certain times of the year), etc. that could be contributing to the residue. Look around your local environment.