I have three shrubs that I purchased at different times, all planted with southern foundation exposure. I have banana trees thriving within three feet of these shrubs. And yet, over ten years, no blooms on any of the three plants, ever. Not one. The plants grow annually, but fail to flower at all. I have twice emailed the seller, One Green World, which is a highly reputable nursery, and have not gotten any sort of answer. Suspect they are stumped as well. I live in Everett, WA which hovers pretty close to a zone 8 for climate, and have an extensive variety of plants which are successful long term. Not a beginner :-)
Feijoa – Pineapple Guava Plants
Certified GKH Gardening Expert
Since you have never had blossoms or fruit, it would seem the plants are not quite happy in the environment.
Feijoa will grow in full sun or some shade locations. They can be grown in several soil conditions but do need a slightly acidic soil.
They do not require much pruning and typically will do well with just rainfall irrigation.
Do you know the varieties that you have planted? A self fruiting variety that has done well for home gardeners is 'Coolidge'.
The plants actually do need a brief period of cooler temperatures in the winter to set fruit.
I would suggest a soil test to help you determine what may or may not be needed.
Here is a link to refresh you on the care requirements.