Thank you for your comments, Gunnar, Erik, Michel, Graeme, Torsten and huib.
Though my friend Mr. Cryns preparing a set of rowers, I would like to describe how I converted mine, in case anybody have a similar problem in the future.
I had already stuck dol pins ( used to fasten the oars ) in the proposed positions and the benches as symmetrically as I could.
Then I copied in resin, Orion rowers this way: Upper body half with hands ( I used 2 different, one clothed and one unclothed) and skirt with legs. ( I also used 2 but it wasn't necessary ). I also copied different heads. By gluing body halves by different angles combined with different heads gives a not so uniform result.
The reason to make the resin copies is that as a material is by far more friendly.
Next step was to glue oars in place. (One of them is scratcing the surface of of the water)
And I was faced with the hardest part. Adjusting the hands of the rowers.
Well it turned out not to be difficult at all. I cut off both hands from everyone's shoulders and gave each rower a specific seat. All the lower hands wanted just a different angle. For the higher hands I excluded the biceps and I connected with a wire. After fitting I filled with epoxy putty.
I have painted the rowers with rather light colours having in mind their low potition.