For the feet I would use two pieces for each foot.
Dado a cross grain recess in the middle of each piece, sized to fit the upright leg/back brace. Like two half laps. Then face glue them together.
I'd use the full thickness and width of the upright to fit in the resulting "mortise". Or, you could make the tenon 1/2" narrower (1/4" off each side). Size the dado accordingly. Use Tite Bond lll or a urethane glue for weather proofing. I always work a couple of coats of glue into the end grain of the tenon, also. You don't want any wicking.
For the leg/back brace, I'd also use two pieces and a looong scarf joint at the bend.
I'm ultra cautious, so I'd make a middle one, too. At least, under the seat.