This is considered unauthorized practice of law and is illegal. Helping a family member is one thing, but charging people for this service is illegal unless you are an attorney. I know pf a few "notarios" and "immigration processors" who have been fined by the state bar of Texas for doing the type of activities you described.
In Florida persons have gone to prison because they crossed the line and practiced law without a license. Another lady was charged with helping persons to commit fraud and also sentenced to prison with a heavy fine. I suggest you find out what the TX law is. The TX Bar Association can probably answer your question.
You are not allowed to fill out immigration forms on your own in the State of Texas and charge a fee. Attorneys are the only one allowed to charge a fee. Accredited representatives may charge a nominal fees under certain circumstance. This will be considered as the unauthorized practice of law. It is also a felony in Texas for a Notary Public to fill out Immigration Forms and charge a fee.
Everyone should be aware that it is illegal for a unsupervised non-lawyer to fill out forms for a fee. This is a big problem and you can cause someone to be deported, for example, without realizing what you are doing. While free help is not "illegal" it is still dangerous. There are things you don't know when filling out an N-400 that could cause someone who thought they were going to be a citizen to suddenly lose even their resident status.
People should always consult an attorney - even if they don't hire one to do the work. It's better to know if there are any red flags for any reasonable consultation fee and then act on your own than to do it on the cheap and possibly ruin your life.
My latest example is a client who paid a notario $200 to file a petition for his wife. She waited six months to file it. He has now lost six months of his life together with his wife if not more because of this.
This is not permitted legally and should not be done ethically. It's like one of the IJs in SA immigration court says, "immigration law is as complicated as tax law, but without a helpful index." Aside from the legality issue, it would not be fair to the person who would rely on your services if something goes wrong.