asking for Nephew's surname change

good day!

my sister is living in japan right now and she wanted to take her son with her to migrate there also. She has a japanese husband who wants to adopt her son. My question is, what are the legal process/procedures for adopting a filipino child? and how long does it actually takes for any results?

One of the problems that they have about this adoption is that the biological father doesnt approve of the adoption and doesnt approve of the surname change. Right now my nephew 7 yrs old, and is carrying his biological father's surname instead of my sister's maiden name. His biological father doesn't give any financial/monetary support for the child. My sister never married her son's biological father, they just lived together for about 2-3 years. She was only 17 when she gave birth to her son, but the father signed at the back of the birth certificate allowing the child to use his surname.

what is the best thing and easiest way to do about this? I am asking you this because my sister is asking me a favor to process the name change, and I dont even know where to start. If she will adopt her own son, does she still need the consent of the biological father even though they were never married?

I also would like to ask how much does this whole process usually cost?

I hope you could help us with the information that we needed.

thanks...

allege abandonment and non-support in the adoption proceedings so that his consent is not necessary.