Teddy, not mentally stable?
Teddy seemed to have some psychological issues!! His issues weren't as pronounced as the ones some other relatives seemed to have, but still...
After his 1st wife died following childbirth, he left the poor baby, Alice, who survived the birth, in the care of relatives. He was so psychologically messed up, he shot a neighbors dog, who dared to bark at him. I'm sure the neighbor just loved him for that!
I imagine being around Teddy 24/7 would have been exhausting.
AVADA KEDAVRA!!!