I wasn't sure if this was the right section or for the technical section.

I'm about to move my last domain from registerfly to namecheap before they go down the drain.

The rest of the domains are in my new namecheap account. The problem is that I have registered two nameservers on the last domain, and all the other ones use those nameservers.

So the question is basically:
How can I transfer the domain and prevent the sites to go down until I can register the new nameservers with NameCheap?

Shall I ask if NC can register the nameservers even before it's moved? Do I have to set up backup nameservers in the meanwhile? Or will the nameservers get automatically added when transferred?

Thank you =)