Are your avocado trees seedlings or grafted? If grafted, you might try to ID them by comparing to the cultivars featured here. Pollination does seem like the most likely issue, but sometimes trees just aren't strong enough to set fruit. Do they seem just as healthy as before? No strange weather anomalies during flowering?

I've never heard of Lemon Meringue mango before, but it sounds interesting! I've heard of Lemon Zest which is supposed to be delicious.