How to ensure fruit trees are more productive?

[Pcan]

I have a lemon and Nectarine tree in my backyard. I am told it is nectarine, though I am not sure. 

Nectarine??LemonPalmsSoil Lemon treeNectarine?Soil NectarineDressinaPotted (Croton?)Potted (Croton?)Peace LilyPalms

1. Lemon Tree: It can be more productive, is there something I can add to the soil or spray to improve its yield?

2. The Nectarine tree. What is it exactly? Is there some nourishment I can give it? It looks ripe, but hard inside.

3. How do I preserve these potted plants which are indoor ones, now exposed to the sun! I have kept them in as shady a place. 

I water them at least once a day, should I water them twice? I am waiting for cloudy rainy weather that Melbourne promises.
4. There is a rose bush that needs some TLC, pic not included.
Too many ants!!!!!!!!!!!!!

Thanks