What do you mean by this
(a) If B1 and C1 have figures (meaning B1 and C1 != ""), highlight all the values in between.
Also,
(b) If either B1 or C1 is inputed (meaning there is one cell is leave blank), highlight all the values which is smaller than the figure.
Highlight all values in the entire column A?

Will values be entered only in B1 & C1?