I'll try to answer.
Leaf curl in many plants, citrus trees included, is a sign of distress. Judging by the picture and other symptoms, I'd say your problem is due to watering. Citrus trees are very water-intensive, but they don't like having soggy feets, meaning they need excellent drainage, especially when potted. A poor (which doesn't mean cheap) potting medium is usually the first cause, followed drainage holes getting clogged by dirt.
You also mentioned 40°C highs (
we are having 27°C at very most now and tomorrow a further drop in temperatures is expected) but how hot/cold are nights? Also have your citrus trees suffered from any parasite recently? Bugs love to feast on their leaves, causing all sorts of issues.
Now let's move to the lack of blooming. Generally speaking citrus trees fail to bloom if one or more of these conditions happen:
-)Winter night temperatures over 10°C
-)Lack of water in late Winter (January-February)
-)Lack of sunshine
-)Excessive nitrates in the ground (due to water content or excessive fertilization)
Check the list and see if it applies to your lemon tree.
Finally the fig tree... yes, they do develop impressive root systems quickly. That's part of their survival strategy.
A particularly impressive root system may also hint your fig tree is grafted: check if there's a notable "junction" on the trunk anywhere from 1" from the ground and up. Fig trees sold in cold climates are often grafted so that would explain a lot.
Rootstocks are often "franks" or "volunteers" meaning plants obtained from seed, which usually are highly variable in fruit quality but are extremely tough and adapatable as far as soil conditions go. It's not uncommon to see volunteers sprout in the most unlikely places after traveling there in some bird's digestive system.
