The 3 samurai are definitely of the following:
- Shimotsuki Ushimaru
- Uzuki Clan Leader
- Fugetsu Clan Leader
- Or the Amatsuki Clan Leader
The others are Kozuki and Kurozumi, totalling the 6 clans of Wano. There is a reason Oda teased an iteratio of the 5 Daimyo in Odens flashback, but never addressed the rest of Wano's history:
They won't be exactly the same as these silhouettes but their decendents. The only question is why 3 and not 4? Kozuki was "dead" by this point, and Orochi ruled here. So I wonder of the 4, which isn't imprisoned here (assuming they are Clan leaders)