2 displacers are more than enough for any VW NM if you bring that many people.
Around two weeks ago we were doing a Bismark and couldn't get it below 50% (sad, I know) due to lack of damage and bad procs, so on the 3rd attempt we simply used 2 displacers and had no problem of sort.
Last week we did ToAU path and used 1 on Fruitloops, then 2 on Morta. Again, no issue of sort.
A friend who is far behind with VW was stuck on Sandy T3 pixie and decided to simply bash it with 5 displacers. He ended up soloing it like a Bunny in East Ronfaure.
Displacers are a great addition for people who joined in late for VW or for those lowman/inefficient groups that want to have a go at it.