Try and book through the Paradise Pier hotel, it has better rates for economy options. You can also book local good neighbor hotels such as the candy cane inn thatvhas a free breakfast with free shuttle and is still within easy walking distance.
Tl;dr: This is doable, but depends on a lot of different factors. Not sure if you're planning to do Disneyland each day, but if yes you're going to spend a decent chunk of that on tickets alone (and have some potential Disney burnout). For your family, 5-day, single park tickets alone will be about £900. Lodging varies widely, budget (£75/day) is absolute no frills. If you're planning to have a rental car and are NOT planning to do all days at Disneyland, look into an airbnb or similar with a kitchen to cook there and save on meals. There are many other cheaper theme parks in the area, plus destination lodgings like Great Wolf Lodge relatively close to the parks where you could spend all day there instead of Disney.
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