Expand your example as it is hard to know exactly what you want.
On the choosen domain you need your NS1 and NS2 records along with matching A records. Any requests sent to these nameservers will be handled by your server.
as said , in registrar you need to use ns1.domain.nl ALONG WITH its ip address. not just ns subdomain. same for ns2.
ask registrar if this is something you can do from whatever access they’re giving you… registries need to know the dns servers and ip addresses.
putting just subdomain ns1.domain.nl wont work. registry doesn’t know where to find domain.nl nor ns1.domain.nl. that’s why the nameserver ip is needed.