Helios Sisters

The Helios Sisters were siblings who once invaded the Doctor's TARDIS.

Biography
After the Doctor fled from the TARDIS on Earth the Helios Sisters possessed a boy named Peter to help them find the Doctor. Upon finding the Doctor at Peter's home they knocked Peter's mother Sally out of her wheelchair, the shock enabled Peter to shake off the Helios Sister's hold over him. Sally then managed to absorb the Sister's powers into herself, which subsequently killed the Sister's. (ST: Suns and Mothers)