If you are the sole owner of the home (and it’s not entirely clear on that point in your post) then you may evict them to get them out. They have apparently lived there for 25 years, much of that while your mother was alive apparently and thus living there with her permission. It is their residence, and has been for a long time. This is not a trespasser or mere guest situation in which you may have them simply ejected from the property. Consult an attorney for assistance with this. California is more tenant favorable than a number of other states and if you mess up with the process the courts may dismiss it and force you to start at square one again.