How to configure access to multiple servers behind NAT?

Question

Domain Name System

The office has a local network connected via a gateway to kerio control 9.0. One external interface, static address. Requires two physical web servers (apache) to be brought out. There are two domains, A-records lead to the external address of the office, but the ports, respectively, are not specified.
How can I make sure that, depending on the requested name, the connection is established with the corresponding server?
(Assuming no additional costs such as purchasing an additional external address.)
There is an idea to set up a redirect on one of the web servers, but I would like a more direct way.