Basically you need to make A records for ns1 and ns2 that point to your server's IP.

(xxx.xxx.xxx.xxx = represents your server's external IP.)

A Records to set at your domain REGISTRAR:
*         xxx.xxx.xxx.xxx     1 Hour
@       xxx.xxx.xxx.xxx     1 Hour
mail    xxx.xxx.xxx.xxx     1 Hour
ns1     xxx.xxx.xxx.xxx     1 Hour
ns2     xxx.xxx.xxx.xxx     1 Hour
www    xxx.xxx.xxx.xxx     1 Hour

CNAME Records to set at your domain REGISTRAR:
panel         @     1 Hour
ftp         @     1 Hour

Now, by doing this, all your clients need to do is point their domains at your nameservers and then they can use Senotra's DNS and domain management features in one place.