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In cases like this, your Mother's Will will state that you are only entitled to your share of the bungalow as and when it is sold, which would be when her stepdad dies or decides to sell.
Until such event happens, you can't get "your hands on" your share. Unless your stepdad or sisters are happy to buy out your share, which I note they are not willing to do, you aren't going to be able to do anything until the bungalow is sold.
I am sorry this is not the answer you were looking for, but it sets out the legal position.