=(G2>0) * (G2<6) * (COUNTIF($G2:$J2,G2)=1) * (G2<>Sheet2!G2) * (G2<>Sheet3!G2) * (G2<>Sheet4!G2) * (G2<>Sheet5!G2)

It allows only numbers greater than 0 and less than 6. The cells are formatted as numbers with zero decimal places, in case someone wants to enter something like 1.4. In that case, it will just appear as a 1. The formula then checks the other 4 sheets to see if that number exists elswhere. If it does, an error message will appear prompting for a different number.

Flyster

excel-matrix.xlsx