The license is mainly a paper thing. Your 20 twenty users should be able to connect.
Then again, if you bought two licenses for two servers with ten users each, but your plan is to use one instance with 20 users, you may be into a license violation.
Very important: this is a technical forum, and license questions are not technical but legal. All answers you get about licensing here are from laymen.
I would recommend that you contact your local Microsoft representative to sort this out. Potentially, you could get into trouble if you are license-audited.