By 5 weeks old they should be able take the outside temps....unless you've kept them too warm inside.
I keep the heat as low as possible after the first couple days so they feather out faster, usually done with heat by 3-4 weeks.
When I brooded inside I'd open the windows in the brooder room to get them used to cooler temps.
Also take them outside to a day pen during nice days to get them used to the outside.
I would also use a 'huddle box', put it in the brooder after turning off the heat(you might have to 'persuade' them to use it) then move it out to the coop with them.
Cardboard box with a bottom a little bigger than what they need to cuddle next to each other without piling and tall enough for them to stand in.
Cut an opening on one side a couple inches from bottom and big enough for 2-3 of them to go thru at once.
Fill the bottom with some pine shavings an inch or so deep.
This will give them a cozy place to sleep/rest, block any drafts and help hold their body heat in.
Do you have an intergration plan?
Might want to read up on integration..... BYC advanced search>titles only>
integration
This is good place to start reading, tho some info is outdated IMO:
https://www.backyardchickens.com/a/adding-to-your-flock