How to create a IoT Project with multiple collaborators?

Hello, this seems to be a question of IAM Access.

I would recommend not sharing your AWS Account ever, but instead creating IAM Users and providing those to your collaborators. This way you can also implement fine grained access control and not share passwords across the accounts. [4]

Alternatively, you can also share access to their AWS accounts via cross account resource sharing (with roles).[1]

Similarly, I'd also recommend for yourself to not use the Root account but instead create an admin account that you log into.[2][3]

I've shared some info below.

[1]https://docs.aws.amazon.com/IAM/latest/UserGuide/tutorial_cross-account-with-roles.html

[2]https://docs.aws.amazon.com/general/latest/gr/root-vs-iam.html

[3]https://docs.aws.amazon.com/IAM/latest/UserGuide/id_root-user.html

[4]https://docs.aws.amazon.com/IAM/latest/UserGuide/id_users_create.html