I am so sorry for your loss and for your situation.  If the funeral is held in a public place like a Church or a Synagogue, I can not see how your step-parent can stop you from entering the house of worship in order to attend the funeral.  But the writing may be on the wall, so to speak, of what is to come in this situation.  So you may want to seek advise from an attorney in your area on the matter and what you can do to protect yourself all around in this situation.  Paying for the funeral can give you certain rights but not necessarily in a public place.  Again, I am sorry for your having to go through this in this time of grief.