How to control mutilpe validators on one property?

Instead of DataAnnotation, Use IdataErrorInfo and customize the error message.

if you have time, just read this article

or

Check the below links

Simple with Example

http://www.abhisheksur.com/2010/06/validate-your-application-using.html

Check this link as well (if you have time)

http://weblogs.asp.net/fredriknormen/archive/2009/11/22/silverlight-4-and-asynchronous-validation-with-inotifydataerrorinfo.aspx