The basics are that my grandmother's house in Southern California has two avocado trees that have been there for 25+ years. Between the drought and a water leak too expensive for her to fix, she shut off water to the back meaning the trees weren't getting any for quite some time and have declined. Now I'm acting as landlord for the property as it is rented out and I want to take action in regard to the trees but I could really use some outside advice on what can be done.

The main tree is below with photos of both here: http://imgur.com/a/PKE7X. They used to be quite full of leaves and fruit but you can see that it isn't the case anymore with one of them appearing to be dead or close to it. That one was always the one with less fruit on it. The other has some dead branches but still has green leaves. A lot are browning at the tips and the few fruit that it produces are stunted. The overgrowth of weeds in some of the photos was recent and taken care of already. A few years ago both were trimmed but it didn't help as far as I know. As of now, from what I've found online researching the issue, my plan is to test the soil pH balance and probably spread some gypsum in the area of the trees.

Any suggestions on what I should do next would be greatly appreciated.