I honestly don't think they know, not for all of them at least. The bombing has likely disrupted their communications with various regions that their groups are residing in and any groups that stopped reporting in makes it unclear if they all died and whether the hostages died with them.
Additionally, we already know that there were a number of other groups involved on October 7th that weren't Hamas and they each kidnapped a handful of hostages. I don't know if Hamas is able to get info from those other groups on the status of things.