First time posting so hope my photos came through.
I have an orange tree in my backyard that was there when I recently purchased my home in SoCal so I am not sure what kind of tree it is.
I have three other trees: one produces oranges all the time (June - Oct), one has small oranges a little bigger than golf balls, and the other no fruit whatsoever. We have had great weather since August, no frosts.

The tree in question produces nice-sized fruit, but as they are turning orange it looks like a lemon is trying to emerge from the bottom of the fruit, forcing the fruit to start to split. I pulled one off today and opened it: dry inside and slightly turning brown. Before turning a little orange, the green oranges are very firm.

The golf-ball sized oranges have not started turning orange (been visible for about 2-3 months), but I cut one open to see if they are some Vietnamese variety I read about and these are very juicy and smell wonderful. OK to eat?

Hope I have provided enough information for some feedback.