Being in a community property state, the correct way to do it, is to split the business income/expenses right down the middle for each of you. Then report that business income/expense on a separate SCH C for each of you, as a part of the joint 1040 return.
With only one of you as the "official" owner from the federal perspective, the business EIN is assigned to the SSN of that one owner. Therefore the owner of the business will use the registered EIN on their SCH C, and the spouse will use their SSN on their SCH C. That will keep things separate, correct, and in perspective so that each of your social security accounts is property allocated their portion of the SE tax.
