My husband pays Estimated Taxes quarterly using a preaddressed 1040-ES form. I have joined the business as a partner and now I need to pay my taxes. Do I use his form (since it has both of our names on it) and combined our taxes or do I need to have my own 1040-ES form? We file jointly.

Since you file jointly only one 1040-ES is needed. Just make sure that when you file you tax return jointly in April, the SS number on your 1040 matches the SS number used on the 1040-ES forms.

On my husbands 1040ES form both of our names are on it, but only his SS #. How do they know to credit my SS# and how much to credit?

When you file jointly your 1040 you provide BOTH of your SS numbers, and you document the TOTAL of both your incomes and the TOTAL of taxes paid by both of you -- there is no need to worry about accounting for how much is yours versus his. You are both legally responsible to ensure that the total taxes paid by both of you is correct for your total income.

Thank you!