Create a multi-account strategy with an account per company. Use consolidated billing to ensure that Any Company needs to pay a single bill only.

Create a multi-account strategy with a virtual private cloud (VPC) for each company. Reduce impact across companies by not creating any VPC peering links. As everything is in a single account, there will be a single invoice. use tagging to create a detailed bill for each company.

Create IAM users for each Developer in the account to which they require access. Create policies that allow the users access to all resources in that account. Attach the policies to the IAM user.

Create a federated identity store against the company's Active Directory. Create IAM roles with appropriate permissions and set the trust relationships with AWS and the identity store. Use AWS STS to grant users access based on the groups they belong to in the identity store.

Create a multi-account strategy with an account per company. For billing purposes, use a tagging solution that uses a tag to identify the company that creates each resource.