The closest resort to Temecula is going to be the Welk in Escondido. There are 3 sections to Welk Escondido, and they are different from one another. The Achilles heel of Welk Escondido is that it is built on a hill immediately beside the I-15 Freeway, so the freeway noise carries right up the hill. But since you are posting in the Marriott forum, and talk about using points, I'm guessing that you won't be interested in Welk, so there's probably no need to discuss it further. Four Seasons Aviara is also not terribly far, and it's an upscale place, but it's not a Marriott.
Don't forget to consider a short stay in Temecula. Temecula can be fun for a day or two. I'll wager that the wedding may be held at an area winery.
I'm assuming you will rent a car. Your choice of airports includes LAX (Horrors! LAX is a madhouse. I avoid LAX if at all possible.), Ontario (ONT), San Diego, Orange County (John Wayne) airport, and also don't forget Palm Springs airport. So you will want to do some homework about flight cost to/from each airport, rental car cost at each airport, and driving time from the airport to your destinations.
San Diego Pulse is not far from Temecula, but it's a Pulse property, so you'd expect small rooms.
If you prefer traditional timeshare resorts, and want to plan 2 weeks (try to - there's plenty to do), I'd aim for Newport Coast Villas and one of the Palm Desert Marriotts. NCV is 2BR dedicated units. The Palm Desert Marriotts have 2BR lockoffs. We have stayed at all of these locations, and they are all very nice properties. (My only caveat is that we are not fans of the Shadow Ridge Enclaves. When we visit Shadow Ridge, we stay in the Villages. But this is personal preference. Desert Villas 1 and 2 are our personal favorites in Palm Desert.)
October is not peak season at NCV or Palm Desert. I don't think you'll have a lot of difficulty making reservations if you plan well in advance.