Is the step parent required to pay child support in the state of Alabama to the step- children?

Typically the children's natural parent is required to pay that support. Not a step parent.

Thank you. Now what percentage will I receive of Child-support, since Im filing an divorce on my husband who is an Marine?

Alimony and child support are two different issues. If you husband is the stepfather... he would only owe you alimony... you should be and have been collecting child support from the child's natural father.

As far what how much it totals is beyond my ability to guess on. Someone else will have to make an educated guess there as there will be factors taken into account at the court hearing that will effect those numbers.

I have two older children with my kids biological father and is receiving child support payments from him. With my husband we had one daughter who is 6 months old and I know I won't receive alimony because we've only been married for 2yrs and 6 months.

Be patient and you will get some more and better answers to that question as more members read this thread.