The "dad" may be able to assert that he is the de facto parent of the daughter. This is basically a claim that he has taken on the role of a parent "in fact." He would need to include both the natural father and the mother in his petition.
The "dad" will need to establish the basic requirements for a de facto parent. The issue is whether both natural parents are willing to agree. If either parent disagrees, the matter will need to be decided by the court.
I would suggest that you contact a family law attorney and get a 30 minute free consultation. You may contact my office and I will be happy to discuss the issue with you right away.
LEGAL DISCLAIMER Mr. Pierce is licensed to practice law in Washing with an office in Seattle and services clients in all parts of Washington. He can be reached at 206-587-3757 or at the email address at piercefamilylaw.com Mr. Pierce is ethically required to state that the response herein is not legal advice and does not create an attorney/ client relationship. Also, there are no recognized legal specialties under Washington law. This response is only in the form of legal education and is intended to only provide general information about the matter within the question. Oftentimes the question does not include significant and important facts and timelines that if known could significantly change the reply or make such reply unsuitable. Mr. Pierce strongly advises the questioner to confer with an attorney in their state in order to ensure proper advice is received.
If Dad were in Florida, I would tell him to file a petition for custody and ask for an expedited hearing if she were not present. If she is present, she needs to appoint him as the sole legal guardian of both of the children or sign over full parental responsibility and custody to him.
The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. Attorney is licensed to practice law only in the State of Florida. Responses are based solely on Florida law unless stated otherwise.
Mr. Pierce's answer is correct about the daughter. However, there also needs to be a court order for the son. That would be through a petition to establish a parenting plan, in connection with a parentage (formerly known as paternity) action.
Legal disclaimer: [In accordance with the Avvo community guidelines, this communication does not constitute "legal advice", nor does it form an attorney-client relationship.]
If the child resideswith the "dad" a non-parental custody petition might be the best way to go. it is substantially easier to accomplish than trying to be declared as de facto parent. If the child is at risk it might be necessary to contact Child Protective Services. But the preferable course of action would be to file a non-parental custody petition if the requirements can be met. I would be happy to give you a free consultation to help you determine what type of legal action would apply to this particular situation.
DISCLAIMER: This answer does not constitute legal advice nor does it form an attorney-client relationship between the questioner and responder. You should seek competent legal counsel in your jurisdiction to address any specific legal concerns you have.