Focusing... help!

[minnum]

I could use some advice on focusing methods. This is still all so new to me, but I'm SO keen to improve.
Anyway, I have setting on Auto focus... I lock the AF point over one eye then re-compose my shot and press the shutter.

Is there another, better way? especially when it comes to getting both eyes in focus?

I know how to change AF points in my camera, but I can only figure out how to change the one AF point (from middle, to side, up and down) ... What if I want to add AF points, so that more little red dots are showing and I can hold them over both eyes then lock the focus! Sorry, I know this is 'novice-talk' to you guys!
I find this frustrating too with group shots as I only ever have the one AF point in the middle.... with group shots, shouldn't they all be there. Am I missing something? Is there some crucial setting I haven't found? lol

Or do I just need a smaller aperture (bigger number)? to get more DOF. It is when the subject's head is slightly turned and one eye is closer to me that it happens, so is it just a matter of having a higher number? In whach case what f number would you suggest?

p.s.
I have attached a photo so you can se what happens to the eye furthest away. The aperture on this was f4 and ss 1/160

Thanks for your help