I have 2 side by side windows with a combined total of 92" r/o, above each one is a double
2 x 10 header and i want to replace them with custom a sliding door, would opening up the headers and bolting a piece of 1/2" plate steel across them suffice of will I have to replace everything?

that would proably work but if it were me id take it all out and build a 2x10 header with osb inside of it to span the distance, then have a jake stud or too on both sides