If the yeast is good you should only need to use one of the packs and save the other.
pitch one smack pack into each.
Do I need one or two packs? I'm not too familiar using pitching rate calculators...
If you are looking to pitch 10 gallons of 1.050ish ale with packs with best by dates probably sometime in august as the latest you are going to need both packs in a 3 liter starter to approach ideal cell counts. I think you would be fine with both packs in two liters but that is under pitching according to best practices.
check out yeastcalc.com enter your batch volume and expected gravity. enter the production date which is stamped right on the pack of wyeast I think. if not that is the best by date and the production date is minus 4 months from there. Select intermittent shaking from the aeration method menu and you can play around with the steps and the starter volumes and see the cell count change.
I would pitch each into it's own 1 liter starter, when they are done on Friday morning or so put them in the fridge to crash. during the boil pull off 2 liters of wort and chill it as quickly as you can. decant the spent starter wort and add the fresh wort. Let that work while you finish your boil, chill etc. when you are at pitching temp just pitch the full volume.