In season 2 of The Flash, you meet Earth 2 Harrison Wells and his daughter Jessie. However, she has no E1 doppelganger.
Most probably because Eobard Thawne killed Harrison Wells too early and took over the identity that Harrison Wells got no chance to bear a child. Also, there is no Harrison Wells in earth 38 mentioned yet or Supergirl in earth 1 etc etc. So it seems every earth don't have the same person's doppelganger.
There probably isn't a Supergirl on earth 1 because Supergirl is originally from Krypton, so her doppelganger would be on Krypton in the Earth 1 universe, the same with Superman. Since doppelgangers tend to be different than each other they may have never come to earth 1 at all. I do agree with the idea that not everybody would have a doppelganger though, because if a person died before having children, like Earth 1 Wells, it would wipe out all of their possible descendants and this would be very unlikely to happen in every universe in the multiverse, leaving lots of people without doppelgangers.