Removing family photos is meant to make the house a neautral space where potential buyers can envision themselves living in, rather than feel like they are visiting someone else's house. That's the same reason very loud colors/patterns are replaced with neutral ones etc. You want people of any background/age etc. to be able to look at any room and imagine it filled with their things and their family.
At the same time if you remove everything and it becomes a clinical empty space, buyers get put off because it's not cozy enough. So you have to find a good balance, there are no hard and fast rules.
Try removing the very prominent and personal things first, or if there are a lot of little things/photos, remove most of them and replace them with more neutral and bigger things like flowers, vases, trays, coffee table books etc.
You can leave some subtle pictures and decorations but basically you want uncluttered and tidy but not empty. For example if you have a mantlepiece you dont want it covered with pictures, postcards, little objects etc. You want to have maybe 2-3 things on it max.
If you have a gallery wall full of family pictures, print/buy some generic artwork and replace some of it with that and leave just a few personal ones, photos you have of scenery/animals etc without people in them are also okay.
Printing artwork is a super cheap way in general to decorate, especially for selling a house. Just search for "free printable art", there are some gorgeous ones, and make sure you get high quality heavy paper.