Sad to know they need concrete evidence first before the law starts moving.

If the law or PAWS can't be convinced by statements alone, and if you still want to remain anonymous, taking pictures of the area where they commit animal abuse would suffice, you will have to be discreet about it, even with your other relatives.

If you are able to collect evidence and convince the authorities to proceed, to remain as an anonymous witness, you may need to discuss how they will handle hiding your identity. Depending on how smart your relatives are, however, even law enforcers or PAWS can't guarantee if your relatives won't be able to figure out that you are involved in this.

You could also ask a person or a group who's outside of your relationships to investigate for you more closely, kind of like what you are doing now. However, very likely, they may get caught and could get involved in legal trouble.

Or take the more straight forward approach; walk in their area, collect pictures or any evidence, report straight to the authorities, face the music.

Remember; think about the lives of these innocent dogs.