Is there any way to block all Mac Addresses except for selected few ? Something like only whitelisted Mac Addresses are able to connect.
Sure. A good place to begin would be Network → Firewall → Access Rules. For “internal” traffic you could go to “Internal Network Firewall Rules” and set the acceptable MACs as authorized and then change the default internal firewall rule to “deny.” On the same page you can do the same thing with “Outbound Firewall Rules.” Peplink has provided good capabilities to do what you want in this regard.
Outbound traffic can be blocked via other means, e.g., Outbound Policies, but I’d probably start with the firewall page.
Will this meet your needs?