Big Sur is fantastic - given the time of year you are going I'd add a day there as driving down might be a bit slow given all the tourist traffic and taking breaks along the way will keep it enjoyable.
Sequoia is ok - but I'd add another beach day. The coast is so lovely that time of year and the June gloom will hopefully be long gone by the time you arrive.
I'd add a night in Big Sur. We like the black beach at Cambria, rock hunting in Jade cove and both sides of Julia Pfeiffer Burns state park, we have picnicked, hiked and played in the stream on the inland side (parking can get busy). We also love Pfeiffer Beach.
Bear in mind anything north of about Santa Barbara is cold water and not nearly as fun to play in if you like being in the water.
Santa Barbara might be a fun stop if you are willing to drive that far. You can go to solvang and eat danish pastries and there is wine tasting and a lavender farm.
Alternatively what about adding a day or two in Sonoma or Napa? They are lovely areas with fun stuff to do.
I'm not a big fan of Pismo Beach. Been to that area a couple of times and don't see what the draw is except it is fun driving on the sand, but car rental companies may not allow you to do that. My kids love the garlic oysters on the seafront in Morro Bay.
Madonna Inn is a must see in SLOtown, it is just so crazy.