Hi, Simos!
I believe you are correct about the naval figures, and I am certain you are correct about the Prussians. Those look like Bill Imrie's Prussian infantry, from his Helenic brand. That was his brand, named for his wife, before he teamed up with Clyde Risley to found Imrie/Risley Miniatures.
The Prussian series had several figures, marching or parading, with a selection of different heads. There were 2 versions of the Pickelhaube with the parade plume, like yours, or with the plain spike. He also produced heads with the grenadier caps of the 1st Foot Guards. Heads, arms, and field packs were all cast separately. Standing, the officers and men were at present arms, and there were also side drummers, a drum major, and an ensign. Parading were the poses you have, plus side drummers.
There was also a dismounted dragoon, standing with the lance that they carried, and a mounted trooper of the Mounted Rifle detachments. Those two were still available in the I/R catalog, up to last year. Last year, the Imrie family stopping taking orders, as they look for someone to buy the business.
Whoever finished these Prussians attached them to the rectangular bases. Straight from the mold, they had the oval bases cast integrally with the figures, that we see in the picture.
The bent rifles suggest that these figures are homecast copies of the commercial figures, though. The casting alloy used was more rigid and not prone to bending like that. That doesn't detract from the attractiveness of the set, it's just a detail that I noted.
Hope that helps, prost!
Brad