Ox kidney...is this ok for steak and kidney stew?

[linspins]

My dad is coming to dinner and really lives steak and kidney stew with dumplings. DH went shoppping and bought ingredients, except neither of us have ever bought or cooked kidneys before. He bought ox kidneys from the fresh meat counter. Are these the ones for a stew? Do I just cut up and put in? It’s going in a slow cooker.
Somewhere in my memory I remember my grandma using lamb kidneys, so I’m worried it won’t be ok.

Beef kidneys are not as tender as lamb, they are large and tough and require long braising over low, moist heat to become soft. They should be cut into small pcs (after removing the surrounding membrane and the fat lump in the middle) & then soaked in cold water for with a bit of lemon juice or vinegar and a pinch of salt for a couple of hours or just boil them for a few minutes and drain before you start cooking them.