Hi Tigbus, you are getting there

When you check the unit stats for the Whirlwind unit, it has 1 barrage point. Those units that can fire add their barrage points together which you check on the barrage table to determine how many templates etc you can use so in your example the three whirlwinds may shoot with up to 3 barrage points.
The process is slightly different from normal shooting, and is presented in the section of the rules on barrages, but in summary are as follows.
- Check how many Whirlwinds can shoot at a single enemy unit. If there is a choice, then you should choose the unit that allows the template to cover the greatest number of enemy units in the formation.
- Now check the barrage table to determine how many templates are to be used, and whether there are any extra BMs.
- Now place the template(s) to cover the most enemy units.
- Roll separate dice for each unit under the template, deducting 1 if the unit is in cover, andplacing a hit marker against affected units.
- Complete any other shooting, placing hits front to back on those units that have not been hit.
- Finally make saves for each unit that has been hit.
I hope that makes sense.