I have a half sister, she's just 4 years old and starting school soon. My mom and her dad separated a few months after she was born. (He didn't want the responsibility and we never had any contact with him since then)
My mom filled out the registry for the birth certificate at the hospital by herself because the biological father was abroad at that time (I guess they submit that to NSO..?)
My mom wrote that she and the father (He's Filipino too) of her child got married in another country (the place where they met) but they did NOT. At the time of the birth, they were still together so we saw no fault at using her father's surname. (He gave his consent) But then they separated 3 months later and, of course, we got furious over that.
But the thing is, we want to change her surname to OUR surname which is MY dad's. He died seven years ago. I know it's unlikely that our request will get approved if we file for a petition because MY dad has no relation whatsoever to my half sister. But what about adoption? Can my mom 'adopt' her to change the surname to ours? MY dad and my mom were married after all, so that means the surname of my mom is MY dad's, right?
P.S. My half sister was born here in the Philippines
If we can 'adopt' her to change her surname to ours, what is the average amount that we'll have spend to do that..?(we just want to be prepared)
Thank you in advance.