This is a 'YMMV' and should be interpreted as such. If I have a need such as 5 in a room for an overnight, as opposed to a longer stay, I will make a comment such as '5 people and would like sofa sleeper and 2 queens'. The ihg card gives platinum status which doesn't count for much but like other hotels it's possible to get an upgrade, so you can ask for it. I used to stay IHG all the time while driving back and forth to Florida, and on some occasions we had 5 or we had people that didn't want to sleep together. We usually got what we wanted. The points themselves only buy standard rooms and once all the standards are gone they stop selling points rooms - my observation, not necessarily gospel, so if it doesn't say sold out, what's left should be upgraded rooms. So if they assign me an upgrade then they have another room that may actually be easier to sell.
A couple of years ago I switched pretty much to Country Inn and Suites because the Hi Ex's were running up there with the Hampton Inn's and trying to be $125-$150 a night - on the road, while I could get a Country Inn for $75 that had a better breakfast at the time (HiEX has improved a bit and both are ahead of Fairfield Inns in my opinion). So I rarely do HiEx any more plus I have a lot of Marriott points to burn and free is free.
So, it's not guaranteed but unless I put 1 as number of people, I'm almost always looking at 2 queens and a sofa bed.
The other option is book the room and call and ask and tell them what you need/want. If they say yes, you are good to go. If they say no at least you tried. And you can slip in I'm platinum but without being demanding.