In general, Marriott has seemed to run each promo completely independent of other promos. The result is that usually you can earn nights/stays/whatever toward all the promos you are signed up for at the same time. So you can most likely get both certs for your two night stays.

Normally, I would suggest calling and asking Marriott just to verify (and it couldn't hurt to do that), but I'm not sure they would really know the answer. They might tell you yes or no, but I'd be worried that they were just guessing or making it up.