It appears that they have never been pruned and are VERY thick, spikey, and possibly need additional maintenance that I don't even know about.

1) Lisbon (?) lemon - very thick, over-growing the back neighbor's fence a bit. Produces big fruit, but from what I would expect, not as plentiful.

2) Nursery says it's a Bearrs lime, based on a sample. I still have doubts - I believe it has a large "sucker" growth (this is new terminology for me). How do I remove this? Is it too late? Fruit seems to not taste as good as I would expect. IMO, little fruit for lots of uncontrolled branches.

3) Mexican lime - in the best shape of them all, but still doesn't seem like it's ever been pruned.

All of these are MUCH taller and thicker than I would like. With all of the thorns and the trees' height, it's very hard to reach fruit and limbs.

When and how should I begin??? Help!

if you could post some pics of the trees and be sure to include a good picture of the lowest branches it will help us get you headed the right direction. Reason for that is we can help you determine if you have rootstock suckers growing from below the graft. Any branches that have leaves significantly different from the rest are typically rootstock. Large thorns can also be a sign of either rootstock growth or that the tree is a seedling. You can prune them to your liking whenever you wish. Doing a prune before spring can limit blooms though.