Sibling liability when deceased fathers business goes to them. His company installed the unit incorrectly. daughter says not her problem

You don't indicate whether the "father's company" is a separate entity (i.e. a corporation or llc), in which case his death affects nothing, the entity (not the daughter or any sibling) remains liable.  If the father ran a sole proprietorship, i.e. the bussiness was not a separate legal entity, it gets more complicated.  The daughter (or sibling) still has no individual responsibility for the father's obligations, but you would have a claim against the father's estate, and may be able to collect from the estate's assets, such as the business, even if they were transferred to the daughter.