Your best help is in the instructions. Personally, I prefer Velux.
Position your skylights such that only 1 rafter has to be cut out. I've never put in 2 so I don't know "how close" to each other they're allowed to be before you compromise structural integrity. If you have a low-pitch roof, you'll need a special flashing kit to give the window more 'angle'. Before you buy anything, be sure of the roof pitch when you go into the store. If you're planning on opening and closing the windows a lot, get a motorized skylite (and I'm not talking about a manual window with a motorized crankhandle)! Using the crankhandle type is no fun, especially if it's 10' or more above your head. Get insect screens with them too. You didn't mentions if you're redoing the roof at the same time. In either case, in addition to using metal (90 degree) metal flashing where the window meets the roof (a key installation step), I first put in snow & ice shield all the way up under the window flashing, down the side, and across the roof for about 2'. I did this first, then put in the (90 degree) metal flashing. (Snow & Ice Shield, I feel, should be used.) Also, you didn't mention if you have cathedral ceilings. If not, you'll have to build a 'well' inside the living room from the ceiling up to the skylite. You'll need to do some math or some asking to see how big your 'rough opening' should be in this particular opening. This is because you'll be building a 'wall' system from the top of your living room ceiling up to the 'roof' in this particular type of setup (ie., no cathedral ceiling).
Best to ya and I'll be hoping to read more from others.