Get one of these- it doesn't need to be this brand.
The chance that your speakers have 70V transformers is slim if it's not a large house but it's not impossible. If you connect the tone generator and you hear sound from more than one speaker, that means it is possible, or that they just wired them together and you may end up with a bit of a nightmare.
If you have a multi-meter, measure the DC resistance on each speaker cable- if you don't have one, buy one and learn to use it if you don't already know (it's not difficult).
Is there any way to contact the previous owner and find out who installed the speakers? If they were in use before, have you seen any wall plates or volume controls near the light switches in the rooms where the speakers are in the ceiling?
The color of the speaker cable jacket and insulation mean nothing, other than red/black or red/black & white/green corresponding to Pos/Neg (in both pairings I mentioned). If one wire is blue, use that as Neg for whatever it's connected to (it's not a common color for speaker wire, but it's out there). Check the speakers that are closest to the head end for the connections- it is possible that the 4 conductor cable goes to the first speaker and the 2 conductor cable is spliced to the corresponding pair in the 4 conductor cable.