#/etc/systemd/network/enp0s3.network
#
[Match]
Name=enp0s3

[Network]
# SLAAC IPv6 for obtaining the default route.
LinkLocalAddressing=ipv6
DHCP=yes

[IPv6AcceptRA]
DHCPv6Client=yes

#/etc/systemd/network/enp0s8.network
#
[Match]
Name=enp0s8

[Network]
DHCPPrefixDelegation=yes
IPv6SendRA=yes
IPv6AcceptRA=no
IPForward=yes
DHCPServer=yes

[DHCPPrefixDelegation]
UplinkInterface=enp0s3
SubnetId=8
Announce=yes

[Address]
Address=192.168.1.1/24

[DHCPServer]
PoolOffset=90
PoolSize=10

This interface is configured analogous to enp0s8 except for

SubnetId=9

and

Address=192.168.2.1/24

#/etc/dhcp/dhcpd6.conf
#
...
# The subnet where the server is attached
#  (i.e., the server has an address in this subnet)
subnet6 2001:2db:8073:e00::/64 {
        range6 2001:2db:8073:e00::2 2001:2db:8073:e00::9;

        # Use the whole /64 prefix for temporary addresses
        #  (i.e., direct application of RFC 4941)
        range6 2001:2db:8073:e00:: temporary;

        # Some /64 prefixes available for Prefix Delegation (RFC 3633)
        prefix6 2001:2db:8073:e10:: 2001:2db:8073:e80:: /60;
}