Should I sand or strip finish and can I put semi-transparent on deck and solid on rails and benches?

We stained the deck a year ago a few weeks after it was built. The workers power washed the deck and used a water-based semi-transparent stain (I don't know the brand).

When we started to use the deck it seemed like the stain was easily marked or rubbed off and over time traffic and sliding chairs left white streaks (see photos). 

One estimate suggested (1) sanding the entire deck - but only the top of bench and rails - to bare wood. (2) Apply wood cleaner and brightener. (3) Light pressure wash deck, rails and bench. (4) Apply two coats of semi-transparent stain to deck and top of rails and bench. (5) Apply one coat of stain to rest of rails and bench.

A: Since they do not propose sanding all of the rails and bench, can they just power wash and put a coat of new semi-transparent stain over the old stain on those bench and rail areas not sanded?

B: I understand that a solid stain can be painted over a semi-transparent stain without sanding so would you recommend a solid stain on the unhanded rails and bench and a semi-transparent stain on the sanded deck, using the same color?

C: Pleased recommend the steps and materials you would use to prepare and restain the deck