Is it imperative that you have multiple authoritative resolvers running (is that vital to your network function)?
If not, I have found that running FTLDNS and unbound as the local recursive authoritative resolver works quite nicely, even on a limited power device like a Pi Zero. I serve 26 clients and 40K requests per day.
Since I like the PiHole functionality on my entire network, I run two separate Pi's, each with PiHole and unbound, and in parallel. One is listed after the other in my router DNS settings, and the first listing gets 99% of the DNS queries. The second is pretty much in standby in case the first Pi crashes.