Hello JDockins07,
Yes, you can use one username and password for multiple companies. You just need to make sure each of them has an active QuickBooks Online subscription.
When you sign up for a new subscription, you'll be asked to create an Intuit account. From there, you can use your existing Intuit account by clicking the Sign in link. You can refer to the screenshot below.
You can also check out this article if you want to consolidate two QuickBooks Online companies (using different Intuit logins) under one user ID: How Do I Consolidate Multiple Companies Under One User ID.
I'll be right here if you have more questions about this.
