Unbekannte Todeszeitpunkte

<Urgroßeltern...Could someone please explain what letter the 6th letter is?

It is called an ess-zet & alternatively can be written as "ss"; eg.
Urgroßeltern = Urgrosseltern (great grandparents). It looks like a capital
"B", but since since no German words start with an ess-zet, if you see
something similar at the beginning of a word, it is a "B" & if you see it
in the middle or end of a word, it is an ess-zet or "ss". Example: in
English he is called Charlemagne, but in German he is Karl der Groß (or
Gross).

You will also see vowels with two little dots over them. The dots are
known as umlauts & change the pronounciation. They also can alternatively
be written without the umlaut by adding an "e". Example: in English the
city is spelled Cologne, but in German it is spelled Köln (or Koeln).
Regards,
Curt