The step mother has no legal rights to the children, however she is in physical possession of the children therefore you will have to file a petition to the courts for custody.
Since the father is in jail, I suggest you make an emergency exparte order to the courts for temporary custody. The judge will hear the petition without the father being present and set another permanent hearing for when the father is released from jail.
Chances are you will be given temporary custody in the interim. You must be able to provide a nurturing and stable environment for the children according to best interests of the children:
Best Interest of the Child
Title 19-A MRSA §1507 (4) provides the standard to be used by a guardian ad litem:
Best interest of the child. The guardian ad litem shall use the standard of the best interest of the child as set forth in section 1653, subsection 3. The guardian ad litem shall make the wishes of the child known to the court if the child has expressed them, regardless of the recommendation of the guardian ad litem.
Title 19-A MRSA §1653 (3) requires the Court to use that standard in making an award of parental rights and responsibilities, and sets forth the standards a court should use in applying that standard:
Best interest of the child. The court, in making an award of parental rights and responsibilities with respect to a child, shall apply the standard of the best interest of the child. In making decisions regarding the child's residence and parent-child contact, the court shall consider as primary the safety and well-being of the child. In applying this standard, the court shall consider the following factors:
- The age of the child;
- The relationship of the child with the child's parents and any other persons who may significantly affect the child's welfare;
- The preference of the child, if old enough to express a meaningful preference;
- The duration and adequacy of the child's current living arrangements and the desirability of maintaining continuity;
- The stability of any proposed living arrangements for the child;
- The motivation of the parties involved and their capacities to give the child love, affection and guidance;
- The child's adjustment to the child's present home, school and community;
- The capacity of each parent to allow and encourage frequent and continuing contact between the child and the other parent, including physical access;
- The capacity of each parent to cooperate or to learn to cooperate in child care;
- Methods for assisting parental cooperation and resolving disputes and each parent's willingness to use those methods;
- The effect on the child if one parent has sole authority over the child's upbringing;
- The existence of domestic abuse between the parents, in the past or currently, and how that abuse affects:
- The child emotionally; and
- The safety of the child;
- The existence of any history of child abuse by a parent;
- All other factors having a reasonable bearing on the physical and psychological well-being of the child;
- A parent's prior willful misuse of the protection from abuse process in chapter 101 in order to gain tactical advantage in a proceeding involving the determination of parental rights and responsibilities of a minor child. Such willful misuse may only be considered if established by clear and convincing evidence, and if it is further found by clear and convincing evidence that in the particular circumstances of the parents and child, that willful misuse tends to show that the acting parent will in the future have a lessened ability and willingness to cooperate and work with the other parent in their shared responsibilities for the child. The court shall articulate findings of fact whenever relying upon this factor as part of its determination of a child's best interest. The voluntary dismissal of a protection from abuse petition may not, taken alone, be treated as evidence of the willful misuse of the protection from abuse process;
- If the child is under one year of age, whether the child is being breast-fed; and
- The existence of a parent's conviction for a sex offense or a sexually violent offense as those terms are defined in Title 34-A, section 11203.