First, know that the plan prices do not include taxes/fees, which vary by where you live. Not sure if that was boiled into your AT&T cost or not.
For the wife, Air Voice Wireless is it. Unlimited talk/text and 500MBs of data is $40 a month. Uses AT&T's network, roaming is free, all she has to do is swap the SIM card in her current phone.
For you, you're a bit harder. Mostly because you tether and very few MVNOs support this AND you use an iPhone, which again only some MVNOs have. A couple of different directions you could go here:
Solavei. Its $49 a month. You can bring your AT&T iPhone5, but I'm not sure if Tmo has moved its 1900Mhz frequency over to HSPA+ in your location, so if you do this, you might want to sell it and replace it with the Tmobile version of the iPhone5. Anyways, its unlimited talk/text and the first 4GB of data are high speed (HSPA+), you may be throttled beyond 4GBs though. As for tethering, it doesn't violate their ToS, but it is "unsupported". This means that your phone has to have the option to tether baked in to use it. I am currently on Solavei, have a Nexus 4, and have had no issues tethering, works fine. I believe the iPhone5 has tethering built into it, but I'm not certain, I've never used one. Solavei has free roaming (including data roaming up to 100MBs) and is pretty decent from my own experiences. That said, it does have some glitches with picture texting... you need to tweak some settings to get it to work, but the instructions on how to do it are online and its not that difficult. I don't even picture text anymore myself... all my photos auto upload to Google+ and then I can just share them with whomever I want quick and easy. Solavei is supposed to be amongst the first Tmobile MVNOs to get Tmo's new LTE, but I'm not sure exactly when that happens. However, using HSPA+, my download speeds are typically around 12 to 14 MBs per second, which is pretty fast anyways (although I came from Sprint's slow 3G so...).
The other option that makes sense for you is T-Mobile's new uncarrier plan. $70 for unlimited talk/text and 4.5 GBs of highspeed data (throttled afterwards). On this particular plan, tethering is free up to 4.5 GBs. They also have a $70 plan with unlimited data, but tethering is capped at 500 MB on that one and you have to pay more to bump that up.
Either way, you are probably better served by selling your AT&T iPhone5 and purchasing the T-Mo version (Unlocked though!). Solavei has some hoops to jump through for it to work for you, but it will probably suit you and is $21 cheaper a month. T-Mo would be smooth sailing, but there is the price difference. Its really up to you, would you rather save the $ or be smooth sailing? Honestly, $21 a month adds up, so I would recommend trying to make Solavei work for you first and if it doesn't, then going to Tmo. Thats the good thing about being contract free... you can just up and switch if it isn't working for you.
So, if you go Air Voice and Solavei, total cost for you is $89 a month + taxes/fees. Just shy of $100 a month in savings.
P to the S: I normally offer folks free Solavei SIM cards (they're $9) because I buy them in bulk for way less. But the iPhone5 uses a nano SIM which isn't available in bulk yet, so I can't help you out there. If you do go this route, please use one of the Solavei sign up links in the first post. Their referral program gives you a recurring $20 a month discount if you refer 3 people (as long as those people stay with Solavei). I'm at 2 people right now imo... so, I wouldn't be upset if you picked mine

. That said, I'm still all about sharing the love too.