Here are the rules for VLANs ..
When you set the switch port interface to access mode, a switch port can be only a member of one untagged VLAN
When you set the switch port interface to trunk mode, a switch port can be a member of only one untagged VLAN but also a member of many Tagged VLANs.
But what you seem to be trying to achieve is use ports 1-7 as unprotected or open ports for ports 8-24 within the switch.
Really seems like something called Priveate Vlan Edge PVE, whereby protected ports will only forward packets to unprotected ports and not other protected ports. .
Here is the definition found in the help text from within the switch.
Clicked to tick the option to protect switch port 8.
That's what we end up with , port 8 is now protected.
Now lets copy the settings from port 8 to ports 9-24, see the circled area below.
now will in the ports you also wish to protect.
Now ports 8-24 are protected ports.
Hosts on these ports will only be able to communicate with hosts on ports 1-7 or switch port 24 onwards, in the case of my switch.
Make sure you save your configuration.