His wife's mum and dad are both British citizens and are in Deir el Balah, and can't get out because of the bombing (Yousaf's doctor brother in law and his family are also over there). Yousaf has repeatedly given public, and no doubt private, messages to Sunak on this subject.
Were they to be harmed (or worse), Sunak is going to be left with either defending a policy that has led directly to British citizens being hit, or reacting in the right way (ie: boot the Israeli ambassador out and do a complete 180).
The first will be absolutely impossible to sustain given that even our media will have to report on why it was a Scots grandmother and her son / grandchildren has been bombed by our allies, and the second would result in all of his backing being removed due to a backlash from the lobby. Either way, he is done.