Not without using containers.
If you continue to use two Pi-Holes at separate IP addresses, then list them both as you are doing.
If you go to a single Pi-Hole at IP 150, then assign that as the first DNS and pick an unused address on your network and assign that as second DNS.
Another option is to use the Pi-Hole as DHCP server, then you won't have to change any DNS settings on the router.