If you wish to use 2 subdomains to other ports, you can use Minecraft's proxy server (it means BungeeCord, Waterfall, Travertine...), and bind subdomain to specifiend in config.yml server. To do that you have to setup your servers in BungeeCord's config:
servers:
pvp:
motd: 'A Minecraft Server PVP'
address: localhost:25566
restricted: false
skyblock:
motd: 'A Minecraft Server SkyBlock'
address: localhost:25567
restricted: false
Remember! Ports must be diffrent than default Minecraft's port (it means 25565), because we will use this port to our proxy. sub1.domain.com and sub2.domain.com we have to bind to server where you have these servers. Now, we have to bind subdomains in your Bungee server:
listeners:
forced_hosts:
sub1.domain.com: pvp
sub2.domain.com: skyblock
domain.com: pvp // You can bind other domains to same servers.
Remember to change force_default_server to true, and change host to 0.0.0.0:25565 Example of BungeeCord's config.yml with some servers: https://pastebin.com/tA9ktZ6f Now you can connect to your pvp server on sub1.domain.com and connect to skyblock on sub2.domain.com. Don't worry, BungeeCord takes only 0,5GB of RAM for 500 players.