Not sure you can do both those parks in 3-4 days. I would choose Yosemite. There are Sequoias in Yosemite but there is no Yosemite Valley in Sequoia National Park. Please don't misunderstand. I really like them both. But IMHO it's very difficult to spend quality time in either of these parks if you are spending all your time driving between them and you have a short schedule.
In Yosemite, as you are about to descend towards the Valley, make sure to pull into the parking lot FOR THE VIEW just after you go through the tunnel. Trust me on this one.
I stayed in a great Escapees Park right near Coarsegold. Park Sierrra rates are $21/night for 30 amp. I remember it as being 15 miles from the Yosemite entrance. But you will need to join Escapees (Escapees.com). Call the park directly to make a reservation.
There is no pool at this park. But you could rent a car in Fresno to get to the parks, or to a YARTS pickup point (such as Coarsegold).
The traffic in Yosemite is pretty bad in summer. Go early, park (if not using YARTS), and ride their shuttles. Get a good park map and also one that shows all the shuttle stops. Wear good walking shoes.
My son and his girlfriend took a 1/2 day horse ride out of Yosemite Valley and said it was great. Reservations would be a good idea in summer.
