Diverging pipelines

I have 3 stages: test, build, contain
There are jobs t1, t2, t3 … for test, b1, b2, b3 … for build and c1, c2, c3 … for contain.

Once all t1, t2 … finish succesfully they currently start b1, b2, … etc and then the same for c1, c2…
Except that I want at this point (b1, b2…) the jobs to diverge, i.e. I want them to be independent.

So c1 should start not when all of the b1, b2, b3… finish but when b1 finished. c2 should start when b2 finishes and so on.

How can I accomplish this?