This paper provides an analysis of the performance of different passive optical network (PON) topologies for the distribution of multiuser quantum keys using subcarrier multiplexing and the Bennet-Brassard (BB84) protocol. PON topologies are evaluated in terms of the achievable quantum bit error rate (QBER) and the useful key rate. Results show that wavelength routed (WR) networks outperform broadcast topologies as the first are not subject to division losses. Within WR architecture the star configuration is the most efficient in terms of network scalability, maximum reachable distance and maximum useful distribution rate. The effect of subcarrier modulation index on the network performance has also been considered showing a similar and non significant impact for the range considered in this paper.