you and the child's father are the parent in the eyes of the state. There should not be any trouble unless your sister creates it. Your sister has no rights to the child, so there is nothing for her to give up.
Hypothetically, she could claim that the child actually is hers, in which case you would need to bring a paternity/maternity action in court to prove your parentage by genetic testing. It would be just like a dispute over who the father of a baby was, except it would be over who both parents were. Unless she does this, however, the legal side of things will not be an issue. Congratulations!
If this was informative, please remember to click "accept" so I may receive credit for my personal time and knowledge. Thank you.
I wouldn't characterize it as "adopting", but one can petition the court to get the mother's name changed on the birth certificate. most courts will not permit an order of this nature until after the child is actually born. Plan on taking the baby home from the hospital. You may want to hire an attorney to put the paperwork together for you, but that's a personal decision. You can basically plan on just doing everything that you would if you gave birth yourself, except that there's a bit more paperwork once it is all done.
DISCLAIMER: Answers from Experts on JustAnswer are not substitutes for the advice of an attorney. JustAnswer is a public forum and questions and responses are not private or confidential or protected by the attorney-client privilege. The Expert above is not your attorney, and the response above is not legal advice. You should not read this response to propose specific action or address specific circumstances, but only to give you a sense of general principles of law that might affect the situation you describe. Application of these general principles to particular circumstances must be done by a lawyer who has spoken with you in confidence, learned all relevant information, and explored various options. Before acting on these general principles, you should hire a lawyer licensed to practice law in the jurisdiction to which your question pertains.
The responses above are from individual Experts, not JustAnswer. The site and services are provided “as is”. To view the verified credential of an Expert, click on the “Verified” symbol in the Expert’s profile. This site is not for emergency questions which should be directed immediately by telephone or in-person to qualified professionals. Please carefully read the Terms of Service (last updated February 8, 2012).