Let all sibs know the situation and run by them the idea of dividing the property, with the arthritic sib getting that fourth home if that works out equitably. But really, unless you know what the options are and what the sibs would want given the options, I don’t think you should decide this.
E.g., the arthritic sib might want the small inheritance as a financial cushion and to move into an apartment closer to town, or whatever.
That is what we two sisters are trying to tell the arthritic sib. Said sib would be so FREE now as far as time and responsibilities go. Just needs a decent job...as inheritance will not last forever.