Not sure what OP's usage is, but doubtful. I'm on a Verizon plan with my 5, a 4S, 3G android, a 4th gen iPad, and a dumb phone. We also have 6 gb of data and use most of it.
OP, depending on your area T-Mobile may be your best bet. Unlocking the devices will be a pain in the rear, but T-Mobile can help you with a workaround. You might not get perfect 4G, but they're trying to get more AT&T spectrum to support older idevices. My boyfriend just switched his 4S over in May and still hasn't gotten anything from AT&T about an ETF. He gets decent service in our area but has had issues while traveling. You can also trade in the old iPhones towards the down payments on new ones with T-Mobile (I.e. trade in a 4S for a discount on a 5).
So you're looking at $50/mo for 1st line, $30/mo for 2nd line, and $10/mo for each additional. Each comes with 500 mb/mo data or it's $10/mo/line extra for 2 gb (+ the included 500 mb) or $20/mo/line for unlimited. So you're looking at about $140/mo before taxes and fees for each line to have unlimited talk & text and 2.5 gb data.
One thing to note is that they may treat tablets differently. I wasn't able to find any info on those.