How to add multiple entities to send a communication message?

I'm designing an input component for selecting multiple entities (E.g. User and User groups) to send a communication message from administration page.

From my perspective UI-1 might create a visual load once user adds the recipients and it might also confuse the users that the selected values are from either one of the category. For the other UI-2 it might have interaction costs.

Which of the following can be efficient and effective? or Is there any better way of doing it?

Note: I don't have the luxury of taking the design for the A/B testing. That is why reaching out for suggestions. Gmail like "to" address field design is not being considered because of technical limitation.