like Bob said, definitely start earlier. At 230-ish, I'd start a full 24 hours ahead of time. You won't have any problem whatsoever keeping 25 pounds of pork hot in a dry cooler for 5 hours or more. Don't be surprised if it takes you 20 hours at normal pit temps. It's going to take some time to get those beasts to temp, so give yourself ample time.
If you can't start that early, then I'd run your temps in the 250 to 275 range at the grate.
If there really are only two (not in cryo, like Bob said), then you may just have a whole shoulder, or a very, very large picnic. My local market sells full shoulders this time of year, because they are popular for puerto rican pernil. I saw one today for 13 pounds, so definitely could be the case. Like Bob said, if they are that big, use both grates. It's basically like having a whole hame on each grate. Not much room for anything else.
Enjoy and report back!