did you have three members before the clan wars started? If I remember right they said to make sure you had 3 members before the weekend the clan wars started so that it could place you clan in a division. If you didn't have three before then your clan didn't get registered but I imagine it would before the next clan wars as long as you have your three members prior to it starting.
Also, make sure they are actually in your clan. To test this, have each of them go to their character and choose to put on the official Clan Tag for the clan (it will be in brackets). If they aren't in the clan, then you will need to have them follow the steps outlined below (from #17 in this thread). If they are all in your clan then what OUHATEME said is likely correct.
11/14 Workaround: If the app says someone is in your clan but they really aren't (ie they don't appear in the clan on the Xbox), here's how to fix it:
1 - Have the clan leader use the mobile app and kick you from the clan
2- Have the user Log into the mobile app
3 - Go to the My Clan section
4 - Click on the Leave Clan Icon
5 - Log out of the mobile app
6 - Repeat items 2-5 until you are no longer in a clan (they may find themselves in a few different clans)
7 - Have the person invite you into the clan you want to join.