Thank you for asking such a great question! Good news is we have a couple options for you to accomplish this.
Option A) You can create a regular email campaign in our 3rd generation editor. You'll want to get both your event's registration URL which you can find out how to retrieve in this article, The Event URL.
Once you've located the Event URL you're going to want to place two buttons in your email campaign. Each button will be linked up to their respected Event URL. This campaign will act as one event invitation for both separate events!
I'd highly recommend using this method as you'll get more design functionality here, along with still accomplishing your main goal!
Option B ) You can create an event invite within the event itself. That invite will already have the event's URL attached to it. You're still going to want to retrieve event #2's Event URL. Similar Option A, you'll want to put Event #2's URL somewhere in this event invite.
With both methods, you'll still accomplish having one event invitation for two events (Or more if you please!). This allows you to keep both event registrations separate while still giving your contacts a "One-Stop-Shop" to register for both events!