Identifying and removal of existing stain

I'm going to clean and restain my nephew's front porch and back deck in Boston. The back deck has no cover so it is weathered to a greater extent than the front porch. The front porch has the remnants of the previous stain job. The surface looks like it was stained with a product that left a "satin" finish on the surface. I have no idea if it was water or oil based. What do you suggest I use to strip it? Also if I use a good stripper will I still need to use a brightener? I really want to do a good job and plan on using TWP Wood Stain to restain both areas.

Additional Info: I'm pretty sure the deck and porch flooring is Douglas Fir...and I plan on using a pressure washer to clean the surface after soaking the deck with either a cleaner or stripper.

Any info would be helpful, thanks!