Open Question: my mother in law owns a house?

she signed half over house to her son regarding a loan of 12 thousand he took out which she let him do but he managed to rack up about 36 thousand pound of debt he now lives in the house and there is 1 brother and 1 sister if something happened to my mother in law how would the other brother and sister stand on there inheritance the house is worth about 1 hundred thousand pounds or would they lose out to there other brother with debts and is living there many thanks for your help this is a uk question thanks