Og and Sichon-Were they brothers

This post has nothing to do with the Yomim Noraim or Aseres Yimei Teshuva. The only relevence to these days is that my son mentioned it at one of our Rosh Hashana meals. (Now why he mentioned it now as opposed to last month when he learned it in camp is beyond me, but being that my son is only 7 I'll give him some leeway).

My son mentioned that his rebbi in camp told them that Sichon and Og were brothers. (This is actually a gemara in Avoda Zarah 65a). The question is that Chazal tell us that besides Noach and his family, the only other person saved was Og who hung onto the side of the teiva. If that is so, how were Sichon and Og brothers? If Sichon was born before the mabul, then he would have died. If he was born after the mabul, then he would have had different parents (since Og's parents would have died in the mabul).

My son claims that his rebbi did not have an answer. However, when I told this kasha to a friend of mine, he pointed to the Da'as Zekeinim M'Ba'alei Tosafos at the end of Chukas. The Da'as Zekeinim says that Og's mother was pregnant with Sichon when she went to live with Cham. Since she was now Cham's wife she was allowed on the teiva and she was saved. Sichon was born on the teiva. I later found that the Maharsha brings down a similar answer as well.