Dear I am afraid for my safety if I did so:
You may be right about being afraid, and they will think of you no matter who turns them in.
Your father has a responsibility to you, and to the adjoining property owners, to keep his property in a safe and sanitary condition and to prevent a nuisance from occurring on his property. The accumulation of garbage over the yard and the drug use, are bad behaviors that may have an affect on your father's property. The town may issue violations because of the condition of the yard. The police may make an inquiry or an arrest because of the drug use.
You should discuss your concerns about the child with a local attorney as well as the harassing text messages. Your attorney should be able to bring your concerns to your father's attention in a way where he will realize that it is in his best interest to do something about his new tenants.
The answer provided to you is in the nature of general information. The general proposition being that you should try to avoid a bad outcome if you can.
If these people are involved in drug traffic or other illegal activities, your father could lose his house. Especially if there is no written rental agreement. Your worries are valid and your father is far more at risk than he may believe. The first attorney to reply has given good advice.
DISCLAIMER: The forgoing comment is for general educational purposes only, and is not legal advice upon which the reader may rely as the commenter has no actual knowledge of the facts of the case, has not interviewed persons or examined evidence, and has not researched the applicable law. The comment is based only on the facts provided, which are extremely limited, and may or may not be true. Complete defenses may prevent the success of any claim. Competent legal advice should always be obtained before taking any legal action or filing suit. Readers employ any information provided herein at their own risk.
Unfortunately you do not have many options. Reports to CPS are confidential and they cannot disclose who made the call. If the tenants harass you or attack you you will be able to get an order of protection. That is about all that can be done.
This advice is not meant to create an attorney-client relationship and is a general anwer to the question posed.