California - Can family do curbside check in and then leave LAX and return?

My family will be coming up from Long Beach off the Disney cruise about 8 in the morning. Our flight doesn't leave until 2. I was wondering if my whole family could do curbside check in and then do something in L.A., return the car and then come back 1 1/2 early to go through securtiy. Flying United if that makes a difference. The only problem I forsee is that the driver of the car (DH) would have to get out to show his I.D. right? Could I jump in the car so that it's not "unatended"? My main concern is that I don't want to give up the rental car until I have too, but want to check the bags in so I don't have to lug them on that shuttle. Any help is appreciated. Thanks.

you can park the car in the garage for $3, take the luggage up to curbside and check it, go inside and check in for the flight (get your boarding passes), and the go back to your car and exit the airport.

90 minutes before your flight, return your car to the off-airport lot, take the shuttle to your terminal, and go through security. on united, if you have gold boarding passes, you can go through the short security line. otherwise, the longer line is waiting. but once you have your boarding passes, they will rush you through security if your flight is less than 30 minutes and you are still in line. you might have to bring this to the ua personnel's attention though, but they usually have staff asking if anybody in line is on a flight that leaves in less than 30 minutes. this is why you should check your bags and get a boarding pass earlier in the day. united at lax does not always follow the 40 minute prior to departure cut off for checking in. sometimes it's 65 minutes (as i learned in april).

if you're leaving from T6 or T8, it's another 15 minutes to the gate from security. 70's gates are considerably less.

Yes, you can usually get away with unloading the bags and family at the curbside checkin and checking yourself in as well (bring a tip for the skycap) while you idle the rent-a-car at the curb, then return the rent-a-car. But if there is a long line (e.g. Terminal 1/Southwest) you won't be able to do this. In such a case go return the car without checking yourself in, have the family check in at curbside (assuming there are <= 2 bags per family member) and return the car and then check yourself in. In either case have them meet you at the departure gate.