This guide shows how to replace the DHCP Server function in pfSense with dnsmasq. You can do this for some or all of your subnets. This addresses a 12+-years old [bug][1] in pfSense.
While it is possible to replace the DHCPv6 Server & RA and/or DNS Resolver functions in pfSense with dnsmasq as well, these are out of scope for this guide. Unbound can run in recursive mode and it has some performance advantages over dnsmasq; generally speaking pfSense seems "happier" with it enabled.
DISCLAIMER: While I have done profesionally network administration in the past, I am not per se a professional network administrator. I'm just a guy with an overly-complicated homelab who's been using dnsmasq for many years. Follow this guide at your own risk—and please take a backup before you start!