It's free to add additional household members to your Monarch account. You can do so from the Household Members Settings page. You'll each get your own login but have the same level of visibility and access to manage accounts, transactions, and budgets. You can even invite a financial advisor or coach.
Invite a new household member to Monarch by clicking on the arrow next to your name on web. Then go to "Members" and click "Add Member."
On mobile you can invite members by clicking through this flow:
Menu -> Settings -> Household:Members -> +
Once you enter an email to send the invite to, they'll receive the invite and you'll receive a confirmation email when they've accepted.
You are unable to invite someone who has an existing account. They will need to use a different email address and start a new account, or delete their existing Monarch Money account.