How do I convert my spouse from a multiple b1/b2 to a citizen?

Although not clear from your question, it sounds like you are a U.S. Citizen, your spouse is present in the U.S. with a B1/B2 visitor's visa, and your wife's parents are U.S. citizens, and your spouse wishes to become a U.S. citizen. With this in mind, the first step will be for your spouse to adjust status to become a Lawful Permanent Resident (to get a "Green Card"). After five years from the date of becoming a Permanent Resident (three years for most people married to U.S. citizens), a Permanent Resident may petition to become a naturalized citizen. As a U.S. Citizen, you could "sponsor" your spouse to adjust status in the Immediate Relative visa category. Alternatively, one of your spouse's U.S. Citizen parents could sponsor your spouse in the Family-Based Third Preference Category, although there is a significant backlog (for most nations, the backlog may be 10 years or longer) for visas to become available, and your spouse would not be permitted to remain in the U.S. while waiting for a visa to become available.