I assume your ASUS support HyppTV VLAN.
Fiber wall socket<--->VDSL2 Modem(Port 1)<--->Asus (WAN Port)
Asus(Port 1)<--->China IPTV
Asus(Port 2)<--->PC 2
Asus(Port 3)<---> Empty
Asus(Port 4)<--->UniFi STB
For PC 1 connectivity to Internet,the easiest is to buy another wireless usb adapter.
or you can do this setup:
Fiber wall socket<--->VDSL2 Modem(Port 1)<--->Asus (WAN Port)
Asus(Port 1)<--->China IPTV
Asus(Port 2)<--->PC 2
Asus(Port 3)<---> Switch <----->An other devices including PC1
Asus(Port 4)<--->UniFi STB
But you need to 2 LAN cable to be drag into your room.(Port 3 and 4)
or
Fiber wall socket<--->VDSL2 Modem(Port 1)<--->Asus (WAN Port)
Asus(Port 1)<--->China IPTV
Asus(Port 2)<--->PC 2
Asus(Port 3)<---> Switch <----->An other devices including PC1
Asus(Port 4)<--->Home Plug1<--->Home Plug2<--->UniFi STB
or
Fiber wall socket<--->VDSL2 Modem(Port 1)<--->Asus (WAN Port)
Asus(Port 1)<--->China IPTV
Asus(Port 2)<--->PC 2
Asus(Port 3)<---> Home Plug1 <----->Home Plug 2<---> switch(at your room instead at the store)<--->An other devices including PC1
Asus(Port 4)<--->UniFi STB
That for you explaination.