I think you need 40 quarters (10 years) worth of credits to qualify for social security, and then the amount of the benefit is determined by the average of the 30 highest income years (120 quarters).
However, the social security system also has rules for spousal benefits -- a spouse who does not work can collect a benefit based on the work income of their spouse.
For more information and dollar amounts that apply to your situation, you should talk to a financial planner. We can't really give that kind of advice on this board.
For income tax purposes, if she has been a homemaker and has not materially participated in the small business, then she should not have income from the business or SE tax/social security credits. You can't split the income just to be equal, she actually has to work for it. And if she has worked for it, you can't really go back 45 years and fix it -- that would require the assistance of a tax professional to see if anything can be done.
