Your husband and the mother of the child have shared legal custody. You are not a party to that judgment/agreement. You have no direct say in the raising of the child. You certainly have normal adult rights and responsibilities when you are temporarily standing in your husband's place, but even those rights and responsibilities are limited by the mother's and father's rights and obligations. If the mother has forbidden you to use certain forms of discipline, for example, or stated that you should not feed the child certain foods, you must honor her requests. Your husband should work out any disagreements, not you.

You do not help pay his child support. He pays child support calculated under the Guidelines or otherwise ordered by the Court based on his and -only- his income. You may support him because child support dips deep, but -he- pays his support. You aren't a party to THAT judgment, either, in other words.

His support of your child from a prior relationship is not a bar to raising his support. The child he is having with you MAY be considered in some circumstances under the Guidelines, but the general rule is "first family first." You will find that the court isn't thrilled that men go out and father new children when the children already fathered are unemancipated, and then claim poverty.

You may find that my answers do not seem supportive of your role as step-mother. You have a role. However, in the world of legal relationships based on divorce and/or paternity matters, the LEGAL relationships and obligations are enforced. You need to put aside your disagreements with the child's mother, unless you believe that she is abusive or neglectful in the legal sense.

Functionally, as many as are allowed. If the child is living with you, you are there to assist and are involved. As to major decisions, if the mother says none, and you are with the none custodial parent, there are practical vs. legal considerations. But your involvement is limited in general.