The brothers were shot and then left to the mob. Their naked, mutilated bodies were strung up on the nearby public gibbet, while the Orangist mob ate their roasted livers in a cannibalistic frenzy.
Ledematen en geslachtsdelen werden afgesneden, tongen en ingewanden uitgerukt, de lijken ondersteboven opgehangen aan een galg. De buit werd triomfantelijk getoond, opgegeten of verkocht
I’m fluent in Dutch and at no point in the supplied link is there any reference to eating anything.
Attempted murder, torture, court, death, body parts being sold, heart being cut out and displayed for years, yes … eating, not so much.
https://en.wikipedia.org/wiki/Johan_de_Witt
There is actually a whole article on their murder, quite extensively detailing the days leading up to their death as the days that follow it (not in English though): https://nl.wikipedia.org/wiki/Moord_op_de_gebroeders_De_Witt
I think most of it was not eaten.
https://www.literatuurgeschiedenis.org/17e-eeuw/straatgewoel-in-de-literatuur
Just the tastiest bits
Some of it is still in a museum.