I saw this film years ago, and don’t know the name of it.
A father is extremely abusive to his daughter after he finds out she has robbed a bank. The mother and daughter scheme to kill/poison him. In one scene they even put a funnel in his mouth to administer more poison.
The Corpse
http://imdb.com/rg/an_share/title/title/tt0065595/
It was also known as “Crucible of Horror”(1971).
You can watch the full movie on YouTube. I posted it below and the funnel scene starts at about 00:47:40.
https://youtu.be/uVK02xXVdd8