It depends, most families I tend to sell them, or most of them, but I have one family which has a mausoleum in the basement, with each deceased family member having a little nook that has their urn and a display stand with something representing their achievements in life and some wall space for portraits, paintings they painted photographs and in some cases certificates, it depends what they focused on. Each alcove also has a chest with any items that didn't fit on the walls in it (seeing as one Sim maxed 14 out of 15 skills in her life as well as climbing to the top of her profession and raising children, you can see how that might be necessary... my personal nickname for her and her sister was the 'over-achievement twins'... it didn't do her much good though, she died at a mere 89 days old, presumably of exhaustion).