step parent adoption child support

I am marrying a man who just divorced his ex-wife. They have 2 children together, plus a third child who is not biologically my fiance's child, but no one, except my fiance, his ex, and a few people, know this. The boy has been raised since birth by my fiance, and believes my fiance to be his father. The boy's biological father abandoned him before birth, fleeing to his home country, and never saw his child or paid any support. The boy is now 8 years old. My fiance and his ex were looking into adoption, when they divorced. His ex now has asked him to still do the adoption. However, I think she is just scheming to get more support. My fiance is under the impression that he can, without actually adopting the boy, somehow "give" the boy permission to use his last name, so that the boy can have the same last name as his brothers, without assuming financial responsibility for the boy. However, I am afraid that he is going to end up paying support for this child. We live in Indiana. Can anyone give me advice??

If he adopts the child, he becomes financially responsible for the child, in all respects.

So, if he doesn't want to pay support or be the boy's father, he shouldn't adopt the child.

(Chances are that if they are divorcing, the court would laugh hysterically at a petition to adopt anyway.)

If mother comes after him for support of the child, then he can ask for a paternity test to be done, and that will solve that problem.

Was the child born during the marriage or before it?

As far as the boy's name, his parents can bestow whatever name they want. The mere use of the name is not going to make a person financially responsible.

Hope this helps answer your questions.