I have never picked a hotel before based on local home prices and I don't think that the OP should either.

As I mentioned in my response to the initial post, I think that of the three properties, the Concierge Lounge at the Torrance Marriott offers Platinums and their guests the best value - I would encourage the OP to call to talk with the properties to find out what services they'll have open during the times that the group will be staying. For instance, I and my family have been disappointed at places such as the San Mateo Marriott during Christmas and New Year's when they'd shutdown the Concierge Lounge - we were comp'd breakfast in their restaurant but it wasn't the full service experience we'd wanted.

I personally think that a family that has 18-20 getting together, all that are adults (boomers to post-millennials), they will have far more options close by (i.e. walking distance) at the Torrance Marriott. Besides what's available at the Del Amo Mall, there's the shops and eating establishments on the southwest corner of Torrance and Hawthorne.

If self service is an interest, there's a BevMo there and also a Smart and Final Extra on the northwest corner if you want to buy items and keep them in the room's fridge. I suspect that the greatest challenge will be finding places that will accommodate a group of this size if they go out to eat that will be open on some of the days during the Thanksgiving period.

From a driving perspective, the Manhattan Beach Marriott is closest to a freeway (the I405). How much that is of value is still not clear since it sounds like most of their activities will be local. Either Marriott or the RI will offer fairly easy access to the multitude of places along the beach (Riviera Village, Redondo Pier, Hermosa Beach, Downtown Manhattan, etc.).

I would also encourage the OP to contact the three properties to see if there's a good/great deal that each hotel might offer a group of that size. Maybe one request would be to comp parking for all in the party - that would be a major savings at either Marriott. Another might be to build a package that includes suites for either the larger family sets in the group or if any bring younger kids.

David