jeffrey milrad asked:
what is the punishemnt for relations with step sister or brother, or mother or grandparent of a step
relative?
The Kollel replies:
If they do not share a natural parent (e.g. his father merried her mother), they may marry each other. A step-mother is forbidden as Eshes Av, and the punishment is Sekilah.
A step-grandmother is forbidden mid'Rabanan. The Halachah of a step-mother's mother is not mentioned in Shulchan Aruch.
D. Zupnik