The presence of germanic tribes in Silesia is a hypothese, not a fact.
Anyway, the nation of Germans do not descend from these germanic tribes anyway, while Poles descend from these slavic tribes that've settled in this area.
We do not have any direct knowledge about Silesia belonging to Moravia and to Czechs before Poland. We know that Krakow did belong to Moravia, and it is assumed that if Krakow did, probably the road to it through Moravian Gate belonged to them as well. It's probable, but there are also roads through Slovakia, so it's not certain. And it's only about Upper Silesia anyway.
The same, there are no infortmation on that Silesia belonged to Czechs, apart that there was a conflict between Czechs and Poland when Poland conquered what would later become Silesia, and that some later czech bishop claimed Silesia and Minor Poland as part of Prague Bishopric. The second thing is really far-stretched. The first thing, again, is probable, but not sure, especially since the tribes of Silesia may have been simply allies of Czechs, or that the conflict occured when Poles reached Czech borders south to Silesia.