That are not lawful
For us Romans
καὶ καταγγέλλουσιν ἔθη ἃ οὐκ ἔξεστιν ἡμῖν παραδέχεσθαι οὐδὲ ποιεῖν Ῥωμαίοις οὖσιν.
The author of Acts indicated that the owners of this girl said that Paul and Silas were advocating or proclaiming (καὶ καταγγέλλουσιν) customs (ἔθη) that were not lawful (ἃ οὐκ ἔξεστιν) for those Romans (ἡμῖν Ῥωμαίοις οὖσιν) to adopt (παραδέχεσθαι) nor observe or do (οὐδὲ ποιεῖν). These men, who had lost the evil spirit that helped their servant girl to predict things, insinuated that Paul and Silas, because they were Jews, were anti-Roman. In fact, the Jewish people had gotten along fine under Roman rule. They had the right to practice their religion, but they could not ask other people to join them. This was what Paul and his group were doing. Thus, this young girl was only annoying them in return. Christian propaganda was forbidden. However, these people assumed that the Paul and Silas were Jewish since they were hanging around with the Jewish people there. Would you be able to tell the difference between a Jewish and a Christian person?