Now I wonder why can't it figure out that PTR record.
Any static A or AAAA entries automatically create PTR records. And if the Mikrotik is the resolver being used by the end of the WG tunnel, it work. Otherwise a public DNS is going to give fail with private address, or the ISP's in-addr.arpa record be return (which some ISP don't bother with so very well could be missing). But I this isn't likely a big deal.
And for some reason remote DNS can't access home DNS. The fun part is that if I try resolve from any computer on remote subnetwork using home DNS, it works. It also works for computers if I use NAT on remote mikrotik to forward UDP/53 to home DNS. Basically, only remote mikrotik DNS can't resolve from home DNS.
In theory, if you have each Mikrotik has it's "brother's" IP listed first as the DNS server, that should work. But DNS doesn't always take the linear path. Things are cached, everywhere, so stale data is always potential when troubleshooting. And not all client DNS resolver follow the rules, e.g. whether they actually respect/use ONLY the 1st DNS server listed. So exactly where things are getting resolved from/to can effect things dramatically too.
It generally easier to have just one DNS server, use that one both side, and have DHCP also return some public DNS as backups. Ideally each DNS server should service a domain – real domain or fake one like ".lan" used by default e.g. "router.lan". What you're trying to do is "cascade" a hostname and PTR lookup across two DNS server, reasonable request, but not really a direct feature of Mikrotik's DNS.
If you really want to maintain separate static DNS for each "home" and "remote", it might be best to qualify all your static DNS enters with some pseudo-domain like ".home" and ".remote", or whatever you'd like, for the records stored on the respective routers. Mikrotik FWD record on each allow you send the "foreign domain" to the other router explicitly. e.g. FWD with regex for "*.home" or "*.remote", with forward-to set other router's IP address & in DHCP server use ".home" and ".remote" in the DNS append suffix.
Script also could sync/create records between two Mikrotik, but pretty sure using just one DNS server will make your life easier.