Sans is Married to Frisk has a daughter named Sira
Sans has a brother named Papyrus
After Toriel’s banishment Sans would go to the ruin door and knock/talk with Toriel
A lot of monsters are trying to get used to surface life but it’s extremely hard for them
Sans and papyrus dad is W.D. Gaster but he fell into his own creation shattering across time and space (First royal Scientist)
Arial was Gasters wife (Sans and Papyrus mom) until she was killed by a human with a gun