I wouldn't bother with it.
A vaccine is a modified, live virus designed to "provoke a response" so the dog builds immunities without actually getting sick.
Since your 2 dogs have already been sick, and beat it, they already have built immunities.
Jack
PS: Your other dogs have also already been exposed, because that stuff spreads like wildfire, and I think they will ALL get kennel cough ... the vaccine will push any over the edge.
How long ago did your other dogs get it?