Hi. My name is ***** ***** I will be happy to help you.
Combining two incomes and dependents could be a good thing, depending on your total combined income. Child support is neither deductible to the payer, nor taxable to the receiver so it will not affect your tax situation. However, the FAFSA could be affected. Usually, if a child's parents have higher income, the child can loose his/her financial aid. When adding your higher income to her lower income, she may loose certain credits but her and her children's exceptions, combined with increased standard/itemized deduction can actually make up for it.
The last major thing to consider is the filing status. If one of you or both are filing head of household, combining your income your tax bracket may actually increase.
Because there are too many variables that could affect your tax return here's what I suggest. Use one of the online tax calculators, first your recreate your current situations write down your tax bracket and balance due and check the credits and than you create a joint return and see where you stands.
I will give you couple of links to online calculators:
Let me know if you have any questions.