Why do i sence evil in my home

It is quite possible, if not likely, you have answered your question already. If your grandmother is involved with witchcraft, then is not the answer to your question rather obvious? The encouraging part of the equation is that you were able to discern it.

Now your question becomes, "What do I do about it"?, and this is an entirely different question.

Pitchfork her!

You cant approach her about it and ask? If you think she might be doing something woodoo hoodoo,it is possible that you experience some sort of energy around the house.Could be dangerous,spirits are for real and I advise you to tell her you feel wierd in the house,dont just attack her with questions,but tell her about your feelings.Tell her about the stange energy ,ask her if she feels it too or is it only you.This way you can make her give you some answers,without you accusing her of anything.How do you sleep at night?

Best person to fight satan is God. I would contact a local Pastor of one of the most spiritual churches in your area and have him come out and annoint the entire house with oil.
Not only will the evil spirits leave, but your Grandma will be right behind them.
God Bless and trust in God