If the house was bought by your grandfather before he remarried and belongs to his personal property, he has the right to dispose of it at will. However, if your step-grandmother has no financial resources, she should reserve a necessary share in her will, so the judge may give her one as appropriate.
If your grandfather bought the house after marrying someone else, then half of the property that belongs to your grandfather and stepgrandmother was originally owned by your stepgrandmother. The other half will be given to you according to the will (grandchildren are not legal heirs, so they are not called inheritance, but bequests). Because the house is a joint stock of two people, one person is half, so it can be jointly owned and used, or it can be agreed to be owned by one party and compensate the other party for the corresponding price.