Flight
San Diego Airport is the closest airport, has direct flights from most places. Very chill airport, right in the heart of downtown. May be more expensive than LA.
Flight
LA is about 2-3 hours from San Diego but tickets are cheaper, making it worth checking out. Especially if you are planning to get a rental car. It's a very pretty drive along the coast down to San Diego. However, just a fair warning this airport is crazy busy!
Flight
My favorite go to site to look for the cheapest flights. You can start here when looking for flight tickets. You can also search for rental cars here, although I have no experience with. Overall, check multiple places before booking.
House Or Rental
Many affordable options especially for families. The Wedding is in San Marcos but if you get a rental car you can stay anywhere. Maybe on the beach? Just a thought...