Sierra passes don't usually close in October due to snow, but it has happened.
Death Valley in October can be problematic for the opposite reason: if can be too hot, particularly in the first half of the month.
If I had to skip anything, I'd start by skipping the Kings Canyon part of Sequoia/Kings Canyon. It's much more of a park for backpackers and hikers than for automotive tourists.
If it were a first time and maybe only time trip, I'd focus on Yosemite and maybe throw in Sequoia for a day or two max.
And I say that despite (unlike SanDeigo1K) Death Valley probably being my favorite national park.