I'm not sure what your point is but OP has a beneficial interest ( i.e. a claim) in the property as he is a beneficiary in his late fathers estate. He could not sell or charge his share of the property until probate is granted certainly but he does have an interest.
WicklowMan - first off my sympathies for your recent bereavement.
So here's my take on it:
Your Soltr says you can sit as you are for about a year and your sister "think the place is worth 300k."
So, do nothing for the next 12 months; continue working on your home in Tipp & get it finished off. In a years time, put the house on the market at your sister's valuation - most likely it won't sell and she'll have to re-evalute what she wants to do.