Creating Host (A) (CNAME) & PTR records for the servers hosting the websites
An A record tells a DNS server what specific IP address to map for a host name. It is the most common type of DNS record. A CNAME (or Canonical Name) record tells DNS that this hostname is an alias of another domain name. This hostname then ends up resolving to the same IP address as the target domain name. A PTR record (sometimes called a "host PTR record") is what lets someone do a "reverse" DNS lookup - that is, they have your IP address and want to know what your host/domain is. The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network.
Creating new primary DNS zones for the new websites
You can use primary zones in one of two ways: as standard primary zones or primary zones integrated with Active Directory. For standard primary-type zones, only a single DNS server can host and load the master copy of the zone. If you create a zone and keep it as a standard primary zone, no additional primary servers for the zone are permitted. Only one server is allowed to accept dynamic updates and process zone changes. The standard primary model implies a single point of failure. For example, if for any reason the primary server for a zone is unavailable to the network, no dynamic updates to the zone can be made.
Allowing zone transfers from Primary to Secondary zones
if a single server is used and that server is not responding, queries for names in the zone can fail. For additional servers to host a zone, zone transfers are required to replicate and synchronize all copies of the zone used at each server configured to host the zone. When a new DNS server is added to the network and is configured as a new secondary server for an existing zone, it performs a full initial transfer of the zone to obtain and replicate a full copy of resource records for the zone. For most earlier DNS server implementations, this same method of full transfer for a zone is also used when the zone requires updating after changes are made to the zone.