Create a formula that combines the field4's as appropriate, as in:
If {table.field4} in ["BOM","DEL","ALH","KER" then
"BOM/DEL/ALH/KER"
else
"MDR/CHN/PNJ"
Now group on this formula field.
It looks like you also want to eliminate duplicates under that grouping, so create a second formula field to group on containing:
{table.field1}+{table.field2}
Suppress the Details and display your records in the second group header or group footer.
-k