Beware of men (prosechete apo tōn anthrōpōn). Ablative case with apo. Hold your mind (noun understood) away from. The article with anthrōpōn points back to lukōn (wolves) in Mat 10:16.
To councils (eis sunedria). The local courts of justice in every Jewish town. The word is an old one from Herodotus on for any deliberative body (concilium). The same word is used for the Sanhedrin in Jerusalem.
In their synagogues (en tois sunagōgais autōn). Here not merely as the place of assembly for worship, but as an assembly of justice exercising discipline as when the man born blind was cast out of the synagogue (Joh 9:35). They were now after the exile in every town of any size where Jews were.