I did see multiple death scenes in one given army, not as reinforcement.
The AI usually does not stock more than one family members in an army,
but it often happens in a siege.

Yesterday I was taking a rebel town,
where there were only three regular units.
I also saw 2 death scenes (one on a peasant, the other on the cavalry).
Now this is quite weird...
Perhaps rules are different in a siege -
whenever a commanding unit fall, there will be a new commanding unit?