Bear has no right to invest (5) = ENDUE
bear = ENDURE
Grave-digger needs stone to be put in position about ten (6) = SEXTON
put in position = anag. ten = X
Give warning to number after earthquake (8) = THREATEN
earthquake = anag. (quake) of earth. Similar to sweetheart = E where the indicator and the letters to be manipulated are parts of the same word.