I spoke to the Diamond Desk and received the following info:
- I'm a Diamond, my wife is not. They will combine the two accounts and give my wife Diamond status and a card with her name and same HHonors number as I have now.
- They will combine the stays from both accounts and apply as credit towards qualification as if it were one account
- My wife is currently enrolled in the 50k gold challenge. He said to have her complete the challenge, then combine the accounts to earn the bonus
- To complete you have to write a letter signed by both of you with both HHonors account numbers and which account you'll designate as the joint account. You must also include proof of "co-habitation", i.e. Utility bill, marriage license, etc.

Hope that helps

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Ken in Sacramento