Yosemite is HUGE and ranges from 4000 feet at the Valley floor to almost 8000 feet at Tuolomne Meadows so temps will be all over the board.

395 and Amtrak are not your only options. You can drive up the central Valley (I-5 or hwy 99). On I-5 -- depending from where in LA -- it is only a 5+ hour drive. So w/ several stops it is still faster than the train/bus.

How many days do you have for this trip? While much of the drive up the east side/395 is pretty, I wouldn't go that way if it took too much time away from Yosemite.

You could go north on I-5 and return down 101.

I've driven up 5 to the bay area a couple of times, it's extremely boring 99 from what I've been reading sounds boring too, no? Days are somewhat flexible, but I was thinking 2 nights. I could go up 395 and come down 99.

Oops--meant almost 9000 feet at Tuolomne meadows.

W/ only 2 nights you simply don't have time for 395 and sight seeing enroute to/from Yosemite.

Even driving fast/boring I-5 both directions, two nights will only give you 1.5 days in Yosemite Valley, which isn't much. Have you booked rooms in the Valley yet? If the Valley is booked up (which is a definite possibility) the whole question is irrelevant.

DW and I have taken a bus (not from LA) to Bakersfield and taken the San Joaquin to Fresno. We took a taxi from the train station to the airport to rent a car. We spent that night at Oakhurst. We went in by way of the south entrance early the next morning and went to Mariposa Grove first.
I did this so that I did not have a one way car rental. We continued north on the San Joaquin to Martinez and ctransferred to the Coast Starlight to go home to Chemult Oregon.
This was the end of a 30 day railpass that took us as far east as Florida.

The San Joaquin\Yosemite bus is worth the extra time. Senior Discount on Amtrak, and while train food isn't wonderful it is edible. Or Pack a favorite buffet for the trip. Coach seats are very comfortable and can be made nearly flat for a nap for a smaller person. For us seniors a rest room at any time is useful.

In early October, you should be in luck with the Tioga pass from 395 to Yosemite being open. The 395 route is definitely the more scenic and iteresting drive. As I understand it, you would want to take 2 days for the drive, not 2 days for the total trip.

Have you been to Manzanar? It is along the 395, and I think would be interesting for the relatives from Japan:
www.nps.gov/manz/index.htm

Lone Pine and Bishop are small pass-through towns along the way that have lodging. Mammoth Lakes would also have off-season prices in October.

Other interesting sights:
Ancient Bristlecone Pine Forest: www.fs.usda.gov/detail/inyo/specialplaces?cid=stelprdb5129900
Devil's Postpile National Monument: www.nps.gov/depo/index.htm
Mono Lake Tufa Reserve: www.parks.ca.gov/?page_id=514

If you get on the 5811 bus from Los Angeles at 1:45AM you can be at Curry Village in time for lunch (11:45).
I used the rental car option from Fresno for the convenience of going where I wanted to go without waiting for a bus.