Charles found with sister’s skeleton in car (7)
I believe the answer is:
chassis
'skeleton in car' is the definition.
'chassis' can be an answer for 'skeleton' (chassis is a kind of skeleton). I am not certain of the 'in car' bit.
'charles found with sister's' is the wordplay.
'charles' becomes 'Chas' (shortened form).
'found with' says to put letters next to each other.
'sister's' becomes 'sis'' ('sis' can be a synonym of 'sister').
'chas'+'sis'='CHASSIS'
Can you help me to learn more?
(Other definitions for chassis that I've seen before include "Car's body" , "Vehicle's structure" , "basic structure" , "Undercarriage" , "an estate may be built on it" .)