Ok, I would base myself within walking distance of the Disneyland Resort.
Get a Hotel with a kitchenette, so look at the corner of Harbor and Katella and the three new Hotels, The Hyatt House, Springhill Suites and the Residence Inn Maingate.. Be careful, as there are multiple locations of the same type of Hotels nearby. All three come with free breakfast.
Use the LA Route 460 bus from the front of Disneyland to get to Knott's Berry Farm, Soak City, Mrs. Knott's Chicken Dinner Restaurant, Porto's Bakery, Medieval Times, Pirate's Dinner Theater and the Buena Park Mall (Walmart). Bus runs every 30 minutes, 6 AM to Midnight seven days a week,and is about 20 minutes in travel time.
Use Uber/Lyft to get to Universal Studios Hollywood, Magic Mountain, a day in Hollywood. (Use Hollywood and Highland as tour dropoff point, and the walk to all the nearby attractions.
Use Uber to Long Beach, dropoff is the Aquarium of the Pacific, and then walk or use the free Passport bus system designed for tourist.
Huntington Beach Pier, Uber there and walk around the area.
Want to head to San Diego? Use ART to the train station. (ARTIC) and take the AMTRAK to Old Town San Diego, and then a short bus trip on MTS Route 9 to SeaWorld (or Uber).. Maybe multiple days in San Diego, AMTRAK is good with checked Luggage, I would look at the Old Town Hotels, the Old Town Inn is nice, and next to the Old Town Transit Center, so the AMTRAK, plus the San Diego Trolley and buses, so easy access to the San Diego Zoo, Balboa Park, the USS Midway and Maritime Museum, Belmont Park and the Pacific Ocean (Mission Beach and Pacific Beach. Or stay in the Mission Beach/Pacific Beach Pier area, Plenty of Short Term rentals are available.
What is your time frame for visiting? aka which month
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How about which airport will you be flying out of? Any preferred airline or Hotel Chain? And are we talking 13 nights? I am willing to get more detailed with more info if you want. Of course, ages of the group, likes and dislikes, etc. would help fine tune the possible working plan