See population stats for western EU countries for the last 100 years. Even if we exclude wars, there's no exponential growth. Thing is, we don't know what demographic policy the Houses are using, and how many colonists initially arrived on the sleeper ships.
Judging from two numbers we have - less than 200 mil for New Tokyo, 220 mil for Manhattan, it's possible to judge how many people can inhabit Kusari and Liberty. For Kusari, "less than 200" is the most populated planet. Even if the other 3 populated planets have around 100 million on average (Junyo probably has less), total population is around 500 million. For Liberty, the numbers may increase since planets like Texas and Denver can have even bigger population than Manhattan. So, it could be around 700-800 million, whcih makes the largest population for a Sirius house (if we don't count Gallia).
