I have nothing against the Catholic faith. Being raised a Baptist there are certain practices I disagree with, but I have never been turned away or or was disregarded by the Catholic church or my Catholic friends. But there is definitely a tension between the two JW and me when I’m at his house.
I’m seeing a number of Roman Catholics posting comments in this discussion, vitriolic Roman Catholics who have proven over the years that they care more about their denomination than about Jesus.
I would encourage you to ignore their advice. Perhaps your friend is tired of Roman Catholicism, and is looking for relationship and meaning. Pointing him back to the RC church would prove fruitless. Instead, point him to Jesus, and be a real friend to him.
Jesus above all, even above denomination (including the Roman Catholic denomination, which considers all other denominations to be anathema).
The nearer your friend comes to Jesus, the more clear it will become to him that JW doctrine is false.
May I suggest that you ask your friend to come to your church (Baptist) with you? Or (better, IMBO) offer to go to his (Catholic) church with him? Joining the JW cult will do him no good at all.