Ah man, look at it like it's a detective-story. To guess whodunit is half the fun. Rikdo-san gives us clues for that reason...
Well. About Hyatt and Elgala having a Solarian-connection... I prefer to think they are just the kind of person Il Palazzo seems to attract: young, twisted women. Maybe or maybe not...
For Excel... that's a whole different story. To imagine she's just someone he picked up at the street is rather strange. Could it be that Excel is related to the royal family? In that case, mustache-man would have recognized her... on the other hand, he's kinda senile and crazy... Anyway, she maybe hasn't those cat-like eyes, But she's the first candidate for a solarian-connection, don't you think?
Well, however. Way back in Vol 13, chapter “A few words I'd like to convoy to you” a certain pedophile scientist discovers – besides lots of other mysterious stuff – this line: Recovery of Frozen Organism. Who or what would that be than, I wonder.
Mince perhaps?
Another thing. What - if anything at all - has Il Palazzo to do with the Shiouji-clan, or more specific: Tenmangu. I think a connection is implied at some points.
Well yeah, however it may be... or not...