I believe this boy is Jakub because the last name is only one letter off which could be due to translation differences. Also, his birthday would put him at the correct age!
I was able to find Jakub's sister because they shared the same last name and both addresses.
This was as far as I was able to go for both Jakub and his sister Chana. I attempted searching "Haftownik" and "Haftornik", and found nothing in any of the databases and websites I looked at. Because both Jakub and Chana had a transport number (12), it is very possible that they were both deported to Chelmno and perished there. However, because we do not know the date of their transport, we can not be sure either way where they ended up. My trail ends here, I hope someone else can follow up with Jakub and his sister!