If two different members are trying to apply using the same email address to apply, and you try to add them more than one of the to the team, one of them is going to get overwritten.
(You can receive multiple applications from the same email address, as this allows someone to go back and re-apply if for some reason their application was not complete or you needed them to fix something or provide more complete information. It also allows them to apply for multiple trips.)
As a remedy, the best option we can offer at this time is for you to ask them to complete the application again, each person using an unique email address.(You can create free ones using gmail or yahoo). To save them time and some frustration, you could copy/paste and send them the text of their prior applications. That way they could just paste the answers back in.