I would think that the health of the root system is paramount to avocado culture in containers. Frequent repottings, root pruning, and a careful selection of a potting mix.

That and ample sunlight in addition to the appropriate fertilizer product and regimen, all of which work together to support a healthy tree crop.

As with orchard apples the right avocado cultivars have to be paired up in order to get adequate fertilization of the flowers - are the two kinds you have known to be cross compatible?

Are both trees flowering at the same time of year? I am near San Jose and have a dwarf variety that produces fruit at a slightly different time as the Hass variety. Here’s a neat website that says that the Fuerte variety flowers a bit before the Hass. https://www.agric.wa.gov.au/spring/growing-avocados-flowering-pollination-and-fruit-set?page=0,2 Its an Australian site so it might be a bit different for us but worth a read.

Here is an excellent blog post that explores avocado fertility Issues. I don't know if any of it applies to your situation, but it’s an interesting read: http://www.epicenteravocados.com/blog/

All fruit trees (including avocados) need to be grafted. If you do not know about this...that is a game-changer. Any quality nursery buys only from quality growers that graft their trees. Un-grafted trees produce either inferior fruit or no fruit....99% of the time.

I grew up with three 20-40ft tall avocado trees in my yard, as well as three 4ft diameter 60ft tall Pecan trees, a couple 12-20ft tangelo Trees, Half a dozen 12 ft tall Banana plants, Half a dozen 60ft tall oaks, three 6-12ft Naval orange trees And a myriad of no less than 3 dozen different flowering plants throughout The front and rear yard. our avocados typically produce every 2-3 years due to temperatures dropping to 12°F-32°F between November and march depending on hurricanes and rainfall here in Central Florida. When our Avocado trees bear fruit, it’s typically 12-30 avocados per tree throughout the producing months. However opposite those productive years are always low production or zero production years. Not certain of the tree‘s descent, but Our avocados are typically well over 2lbs each and very large.

I recommend to limit your fertilizing. I don't grow avocado trees (too cold here), but have other fruit trees. I never fertilize them with synthetic fertilizers. They are always loaded wit fruit.