So is the dinner tomorrow? If it is tonight how was it??
The baby backs ribs are usually a guide of 2-2-1 (2 hrs smoke - 2 hrs foiled - 1 hr back in smoke to set the glaze) at 225 degrees.
I split my chickens in half, others do a spatchcock (hope spelling is correct). It is a mix on to brine or not to brine. I am on the fence. I usually figure around 2.5 - 3hrs for split chickens at the 225 temp, you can turn it up a bit, maybe 250-260.
So if it was me. I would smoke the ribs for the first 2 hrs foil and put back in on the top shelf and then put the chickens on one of the 2 shelves below the ribs for the 2hr foil. Check the chicken temp (target >165 for 3 min, some like to make sure it is really cooked and will go to 175. It is up to you.) when I check the ribs in the foil. If they are ready to set the glaze remove from the foil and continue to cook the chicken if needed. If the chicken skin is not crispy, if that is what you want, put it under the broiler for a couple min to crisp it up.
I find that the MES tends to retain a lot of moisture inside of it. I don't put much water in the one I use at work. Some have used a playground sand mod, I never have.
Hope this helps. Happy smoking