You can't add 4 nameservers in a "fallback" configuration with a registrar. The order that the nameservers are looked at is entirely arbitrary, as it is designed that way for load balancing purposes.
It is probably unwise to dynamically update DNS servers, as this information should generally have a long TTL, and will cause issues with registry settings etc.
Depending on what you are trying to do, you might be able to get away with having a set of reliable nameservers and then dynamically redelegate the subdomains NS records, although it would be more efficient to re-delegate the A records directly.
(Also, this is probably not the best place to ask for DNS advice - I asked a similar, albeit more complex version of this question, and was given incorrect information. You may have better luck at serverfault.com. Before migrating it though, you will probably need to provide a better description of exactly what you are trying to do and what you mean, ie define "Update Dynamically", how you plan on updating it dynamically and advise why you are looking to update nameservers dynamically rather then A records )