Citrus can be pruned to whatever size and shape you like; but if you prune it hard, you will lose a lot of the fruit for next year. If it were mine, I would prefer to prune it so that I could harvest the fruit without a ladder; but it is best to start that when the tree is younger. You didn't post a photo of the avocado; so I will assume it is an older tree and rather large. Again, I prefer a smaller height for my avocados; but I started pruning when they were young.

Unfortunately I don't have the option of starting young. I am thinking to prune the 2 bigger citrus trees back hard, as you say, so I can pick the fruit. If it means a smaller crop next year that's fine - I just wasn't sure if it was a good idea.

The avocado tree I am less worried about for the moment. It's a strong well balanced tree and the fruit doesn't seem to be overloaded for it's size.

I have a lemon tree and it had been neglected for over ten years. It was a disaster, the branches grew in every direction and it became a tangled mess. It has also not been watered for several years, and I have read that in citrus plants this contributes to tangled growth problems.

Your orange tree looks great compared to my tree.

Pruning an older tree to prevent it from growing taller can be a tricky thing. You should probably let it be. I would though prune out branches if they are crossing in between through other main branches of the tree, because this can lead to the smaller branches later running into each other and a tangled appearance. Sometimes it can be a difficult decision to decide which branches to prune out. You want to promote a good outward branching shape, and space within the mass of tree branches, but sometimes this could mean cutting out a branch that is the base of a huge section of the tree.