You should never over lap channels that causes co-channel interference. If you have to then as stated above the AP's that are farthest physically apart should use the same channel.
Also, I would turn off 2.4GHz unless you NEED IT and even then you probably don't NEED IT on all 4 AP's. Try just on 2 AP's to reduce interference and see what happens. Many cases in our offices I have either completely turned off 2.4 or I have it on only 1 AP and absolutely no complaints about wifi since I did that.

@JaredBusch said:

With that last post You are comparing phone to tablet. Two different things.

I see how you have drawn that conclusion but I don't believe that is what was originally intended.
Look at it a bit like this:
1st image Apple promote ditching the stylus
2nd image Apple have built a stylus (type device) and are promoting its purchase.

If anything, it's an unfair comparison between touch screen technologies

This was a good article on the subject of Apple and expectations.
http://www.nytimes.com/2015/09/10/technology/personaltech/apples-iphone-still-breaks-the-rules-eight-years-on.html?_r=0