I would start by reading the documentation on docs.vyos.io and the documentation for pfsense. Then you can look at how the products are used in your architecture and see if functionality can be transferred.
It is impossible for outsiders to say anything useful about your architecture and the use of pfsense and vyos in it.
For me, pfsense is more a corporate firewall with all its filtering features and vyos is more datacenter centered with its routing and firewalling. Though you can exchange them, it’s a matter of taste.