I'd go prot/ret on the paladin and Tank/DPS(both unholy) on the death knight. This lets you switch tanks for when one would be better than the other while still having the utility of an unholy death knight. You can always respec the old fashioned way if you want to go holy for a while, but when you have a druid and shaman available I don't think that will be often. This also gives you the option of having two tanks which may prove useful at times, although it isn't necessary. For the shaman make your second spec resto, then you can choose on an encounter by encounter basis which char between your druid and shaman should heal and which should dps.

Druid tanks should have more HP than other tanks while in bear form. If that 17k hp is in bear form something is wrong.

There are a lot of BoE epics you can get, just browse the auction house. The crafted ones are generally good starter ones for heroics but you want to replace them with either heroic epics or early raids. If you're lacking defense or EH the titansteel pieces(and blue BS stuff as well) generally comes with a ton of stamina and defense, as well as probably having more armor than what you have due to being a higher ilvl. I'm not sure specifically what to get for feral tanks, but I'm sure there are some leatherworking craftables and probably some boe raid drops that are good for you. I know there is a good druid cloak but I forget what it's called.

I started heroics with my DK(playing solo) at around the stats you have now, maybe alittle less. Granted DKs have been nerfed since then, but worst case you just need to buy a couple boe epics and you'll be good.