According to the Numbers 27:1-11, widows and sisters don't inherit at all. Daughters can inherit only if their deceased father had no sons. Isn't this unfair to women?

This is not the entirety of the case. Normally daughters received their share of the family estate in the form of a dowry given them when they married. Sons later divided the estate when father pased away. Because of the dowry, Old Testament inheritance laws did not actually discriminate against women, since they were given their share of the father’s estate when they left home, and after marriage became members of their husband’s family.

In the Quran 4:77 it says “Unto the men (of a family) belongs a share of that which parents and near kindred leave, and unto the women a share of that which parents and near kindred leave, whether it be little or much, a legal share.” So daughters are entitled to an inheritance but according to 4:11 they are only entitled to an amount equal to half that given to a son.