Looks pretty clear to me. It's a yard wide and sold per linear inch. So you'd have 2 identical line items on same order or two separate orders by doing what Floyd says. Frankly that is a very attractive price for leather. As far as the 'site calc' all you have to do is put the number in the search box, add teh hit to the shopping cart, click proceed and then in teh shopping cart change the quantity to 24 for each line, for a 2-foot piece. I tried it and did not have any problem. The final price is fine - if you go to Tandy Leather to buy "sides" of upholstery quality you will find them for $4.00/SF -BUT- you will have to buy 50 square feet most likely to make the minimums. The idea that you can get top quality upholstery leather that 100% matches what you have in for around $5.00/SF looks real good to me.
As for the seat cushions, just repair them with upholstery batting and foam from a fabric store such as Jo-Ann Fabrics. For those of you *not* tearing into your seats at this time here's some detail. Jo-Ann fabrics has in stores or will order for you either high- or low-density upholstery foam. You can tell what's in your seat already when you pull the covers back and pinch it with your fingers. Consider getting a scrap of each from the fabric store so when you check your foam out you can tell the difference. It would not surprise meif GM used different densities on different parts of the seats - and it wouldn't surprise me if it was the same density all over. Your real problem is that since they (actually for the Riviera it was Lear Corporation I was told - see http://www.lear.com/jsp/common.jsp?page=al_co_companyoverview) make the seats, they had cushions molded to the shapes needed. You're not in a good position to do that. But you have good options.
Basically, you buy or make up a block of foam somewhat larger, trim it down carefully with a bread knife (BE CAREFUL!!) or electric carving knife (if you can sneak it away from Spouse - again BE CAREFUL!!) and then cover each trimmed block with a sheet of polyester batting. When you put the cover back on, the batting will smooth out the irregularities in the foam block. If you want, you can modify the seat padding by putting higher density foam in, for instance, the 'small of the back' area and/or the sides of the cushions (to hold you in place better in the corners).
As far as the replacement panels are concerned, you may need to have an upholsterer do the job depending on what sort of sewing machine you can get your hands on. That said - if you are familiar with your home sewing machine, then what you need to know about using it to sew leather is here;
http://www.ehow.com/how_2038402_sew-leather-standard-sewing-machine.html
By the way, the markers mentioned in the article are Sanford "Sharpie" type. You can get the needles for $5 plus s&h from http://www.tandyleatherfactory.com.
In general, you will have to diassemble the seats to see what's up, then using the foam, batting, a bread knife and 3M spray adhesive (don't buy the offbrand stuff unless you REALLY know what you are doing, it's not worth it)
Or let an upholstery shop do the work once you get the material if you don't want to do it yourself. You pull the seat and bring it to a good upholsterer, with the replacement material, I am confident you'll be able to strike a decent deal for the work - but be sure you act curious so that they explain to you what they'll do, how they do it and what materials get used. You bring the good new replacement material, it takes a lot of hassle out of the job for the upholsterer.
Based on you being on Long Island, Steve, if I were you I'd find a sole-proprietor type upholstery shop and have them do it. You might call in advance to tell them you'll get the leather straight from GM and stuff, and maybe to work out pricing. I think your BEST bet is to ask at a couple new or used car dealer body shop managers this question: when they have a used car they want to put on the front line but it has an upholstery rip, who do they take it to to be "sectioned." (to have a section of the fabric seam-ripped out and replaced)
So I hope this helps and that you get this done in the next few weeks. Let me know what you think of all this an let us all know hoe it goes, post pics of the repairs too please.
Albertj