You could do a super list class
public class returnList
{
public List<GrpUsersResp> GrpUsersResp;
public List<GrpUsersResp2> GrpUsersResp2;
}
returnList toReturn = new returnList(){GrpUsersResp = GroupAllReferrals(Req), GrpUsersResp2 = GroupAllReferrals2(Req2)};