Chaining .add()s creates a sequential Flow. For parallelism, use the needs parameter:
from jina import Flow
Flow().add(name='p1', needs='gateway') \
.add(name='p2', needs='gateway') \
.add(name='p3', needs='gateway') \
.needs(['p1','p2', 'p3'], name='r1')
p1, p2, p3 now subscribe to Gateway and conduct their work in parallel. The last .needs() blocks all Pods until they finish their work. Note: parallelism can also be performed inside a Pod using parallel:
Flow().add(name='p1', needs='gateway') \
.add(name='p2', needs='gateway') \
.add(name='p3', parallel=3) \
.needs(['p1','p3'], name='r1')