There is a basic two step approach generally used here in Clark County to help couples such as you with stepparent adoption. The most simple and least costly approach is to contact the paternal father if possible and ask if he is willing to relinquish his rights voluntarily. You can offer him a variety of incentives to do so such as forgiving child support arrearages and reminding him that relinquishing his rights will absolve him of responsibility to make any more payments in the future.
If he is unwilling to relinquish his rights voluntarily, then you must petition the court to terminate his parental rights, which involves proving to the court that it would be in the best interests of the child for them to do so. This requires careful consideration and knowledge of local case law, and I recommend consulting an attorney to help you with that.
Once the father's parental rights are terminated you can file the petition to adopt.
See the link below for more information about terminating parental rights in Nevada.
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