If it's really around 80-85 you can shut off the heat. I believe next week is going to be cooler, at least here in Wisconsin, so you may want to keep up the heat. My gosling are about a week old. I will provide extra heat for another few weeks. Probably mostly at night here after next week.
I wouldn't put them with the chickens, they may peck them. They definitely wouldn't want to keep them warm.
My older geese chase the chickens and ducks away from their area. You may have the same problem if you want to keep them together.