I assume this to be an out of wedlock, extra marital affair child. Her husband.
You now only have physical custody, but both you and your husband have equal custody rights to the child. That means he has a right to have physical custody too, and will not get into any trouble if he physically takes the child into his care. If you are afraid he might take the child, you will need to obtain a temporary custody order, signed by a judge, to make sure you become the custodial parent. That said, depending on your husband, the longer you have physical custody of the child, the more difficult it will be for your husband to obtain legal custody should you divorce.
If the biological father does not have have legal custody, then, no, he can't.
The biological mother has presumptive custody, at least until a custody order is hammered out in court.
Generally, if married he has custody rights equal to the mother unless she has brought a petition for sole custody in his absence. If he is not married his custody rights must be established by a court order.
the person who has physical possesion of the child.
If the mother has legal custody but leaves the state and doesn't have physical custody of your child then that must mean the child is with someone who doesn't have custody. I assume you are not married. In that case, you must establish your paternity in court and request legal and physical custody. If the mother has left the state without taking her child with her the court will certainly want to know who the child is with and will certainly consider awarding legal custody to the other biological parent, you.Perhaps you can convince the mother to consent to your getting legal and physical custody. If not sole custody, then joint legal and physical custody.You should consult with an attorneywho specializes in custody issues. The attorney can review your situation and explain your rights and options.
You have to be established, legally, as her biological father so if you have not done that do that first. Have DNA tests done if needed. Then you can apply for custody or visitation rights.
Not without the permission of the child's biological mother. When a couple are not married and there is not a custodial order from the court, the law presumes that the mother has sole custody of the child in question.
Most likely not. If the mother had sole legal and physical custody and had the "step father" adopt the children without your knowledge - the adoption would be voidable. If he is illegally holding the children against your or their will, that is considered kidnapping in many states. Get the state involved.
Depends if it is a single trailer or a double-wide
Unless the mother is unfit she will get the baby.