How could Kyle reese be John Connors father when he come from the future. Technically if John is Kyles son it would alter the timeline and john would be different from the military leader that saves the human race. Also Myles Dyson creates the terminator from the arm he finds in the hydraulic press. Again the timeline will change and terminator may be stronger. Here is my theory;
Kyle Reese is a Vietnam veteran who suffers from PTSD. Going nuts and struggling to sleep he starts building a t-800 prototype. Finds Sarah Connor working in the resturant. Falls in love but his delusional mind starts to construct the story of the T-800 and john Connor. He activates the machine and the first Terminator happens. This allows the second movie to happen and gives Myles Dyson to build the terminator instead of making great cleaning products.