User... Do not create multiple threads on your issue. It actually works against you as any advice gets scattered around and a coherent conversation cannot develop as easily...
Two users should never share the same account across two phones. As you've seen it will deliver SMS and MMS to both devices despite different numbers. The same Skype contacts and conversations, the same calendar, emails to/from Outlook, etc. It may cause issues around backup and restore. Any advantages are far outweighed by the hassles, loss of distinct data sets and unintended lack of privacy which this causes.
Whatever you two do want to share, such sharing can be had on an ad-hoc basis without resorting to sharing one account. If it is to share App purchase history, it still isn't worth it. FWIW, if you are in the US it is a simple matter to sign up for Bing Rewards and use your accumalating points to get gift codes and stuff your Microsoft Account full of credits. I almost never pay cash for an App on Mobile, PC or Tablet.
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