I'm not sure one can state much about the fruiting of pineapple guava/feijoa that IS normal!

While subtropical in origin, they are quite cold tolerant and are grown here successfully in zone 8. But while they need a certain number of chill hours to produce fruit, too cold a winter will limit fruit production. Conversely, so will too high summer temps - periods in excess of 90 degrees. Drought can also be a factor. Ideally, most reliable fruiting will occur if located coastally or in a fully Mediterranean climate. And with any necessary irrigation

Then there's the pollination issues. Some cultivars are self fertile......most are not. Do you know what cultivar(s) your 4 trees are?

Depending on climate and type, feijoas can flower from mid spring into early summer and fruit can ripen anywhere from four to seven months later. Fruiting in midwinter is not unheard of.

I am located in zone 8B....I think? I'm in Paso Robles, CA. I see lots of them locally that produce fruit so I know I'm in a zone that can.

No clue what cultivar the trees are from. I bought them all at the same store so I assumed they were not self-fruiting and the 4 trees were all from the same location and just clones of one another.

I bought them as 5 gallon trees so it just seems really odd that after 10 years they finally decided to do something. The other odd thing is there hasn't been any flowers on them since the spring.

Have a look at this: Feijoa – California Rare Fruit Growers, Inc. (crfg.org)