At 9-1/2 weeks they will survive those temperatures without any acclimation. I'm not convinced that acclimating them will even make them more comfortable. Some animals do extremely well in colder weather. I believe chickens belong in that group once they feather out.
Probably more for your benefit than the chickens you can take them out during the day and see how they do. That will probably boost your confidence more than anything I can say.
If you want to make them lap chickens they are probably easier to tame if they are inside where you are more comfortable playing with them.
Many of us find it easier to integrate when they are younger as compared to older. You may be beyond that potential benefit. Some of that depends on what your facilities and integration techniques look like.
Just to make sure I understand, two 16-week-old-boys and four 9-1/2-week-old boys. A mature rooster sometimes helps in integration and usually does not hurt. Who knows how your immature cockerels will react. This assumes your younger ones have not hit puberty yet. If the younger have hit puberty they are likely to be seen as a rival by roosters or older cockerels, which could cause a problem. Even if you remove the two older cockerels the older pullets may pick on the younger ones as they are entering puberty. Or those younger boys in puberty may bother the older girls. Another reason to not wait too long to introduce those younger birds.
I don't raise mine the way you do. My brooder is in the coop and my broody hens raise their chicks with the flock from Day 1 so the chicks grow up with the flock. I have three different coops/shelters where they can sleep which helps in integration. I have over 3,000 square feet in outside room and weather where all that room is available practically all day every day of the year. I don't have integration issues but I sometimes (not always but sometimes) have cockerel puberty issues. I have no idea what your facilities look like or how much room will be available in your Wisconsin winter. If you are going to use the "see but don't touch" method, I think I'd want those two cockerels gone before I let them out of that.