If her legal guardian (probably her parents) consent, an adoption could be simple. If the present parents will not consent, you would need to litigate the issue.
You should speak with an attorney that practices adoption law in your state for more information. Perhaps you could be awarded a guardianship rather than having to adopt her.
Spouse indicates that you're married. No, it is not illegal for your spouse to get pregnant.
Your sister-in-law is not related to your spouse unless she is your spouse's sister.
Your sister-in-law may be the sister of your spouse. In that case, her sister is either your spouse and the mother of your children, or she is another sister of your spouse and your kids aunt. Your sister-in-law may also be the wife of your brother. In that case her sister is not related to you or your children.
When your sister-in-law is the sister of your spouse, her sister is also your sister-in-law, unless she is your wife.When your sister-in-law is the wife of your brother, her sister is not related to you.
She leaves her spouse.
Your sister-in-law is either the sister of your spouse or the wife of your brother.
That falls under the category of tough luck. If the spouse can not afford to move, the other would have to agree to let them stay. If they do not agree, the other has to go.
If your brother-in-law is your spouse's brother, then his sister's daughter is your spouse's niece, and your niece, too. If your brother-in-law is your sister's husband, then his sister is not related to you, and neither is her daughter.
There are two ways you can have a sister-in-law.Your sister-in-law is the wife of your brother. In that case, her husband is related to you. He is your brother.Your sister-in-law is the sister of your spouse. In that case, her husband is your spouse's brother-in-law but is not related to you.
One can find information for military spouse education when one goes to the website of militaryonesource. On this site, one can get information about military spouse education and career opportunities available.
Your sister-in-law is either the sister of your spouse or the wife of your brother. The parents of the sister of your spouse are also the parents of your spouse and so are your mother-in-law and father-in-law. The parents of the wife of your brother are not related to you.
The English language has no special term for the siblings of your cousin's spouse, other than calling them "my cousin's brother-in-law" or "my cousin's sister-in-law."