Two Data Validation Rules In One Cell

Create a Data validation rule using Custom:

Formula:

=AND(OR(C5=1,C5=2,UPPER(C5)="B"),COUNTIF($C$5:$C$40,1)<=1,COUNTIF($C$5:$C$40,2)<=1,COUNTIF($C$5:$C$40,"B")<=1)