adding SSD(s?) and HDD(s) to Alienware R8 and R12

My son's R8 has a 256 m2 boot and a 2tb HDD. We want to add a 2tb ssd, will that be completely compatible?

Also I have a R12 with a 1tb m2 and a 1tb HDD, I have a HDD that my wife's co worker filled up with some stuff for me. I have an external "cloning" port I can access it with, but I'd rather just install it. I think the R12 only has the 1 - 3.5 bay, is there a way to get or purchase another one that I can swap out one of the 2.5 bays for?  I don't want to buy a SSD to clone from the 2tb hdd., It was a purchase from some time ago, and I'd like to get some regular use out of it, and its pretty full there's no way to combine all that is in my current hdd with it.