Network traffic for the multi site-to-site VPN paths

Hi,

We are using PIX and Cisco Router to build up the site-to-site VPN for the following network ( remote offices use PIX while central office uses Router ):

1. One remote office and one central office, and the central office has two ISP lines, called ISP01 and ISP02; to build up the ISPs resiliant WAN network.
2. Internet site-to-site VPNs are built between the remote office and the central office, one site-to-site VPN for each ISP line; hence two site-to-site VPN tunnels in each remote office ( or in each ISP line ); and so two site-to-site VPNs tunnels in each router of the central office ( totally 4 vpns ).
3. the LAN environment sets up the Multi HSRP for establishing the WAN HA solution; hence a default ISP line is used for each remote ( view from central office );
4. Due to the above configuration,( view from the central office ) only one site-to-site VPN tunnel is used at each time from central- to- remote office.
5. however ( view from remote offices ), is it also only one site-to- site VPN tunnel used ( the default vpn tunnel by central office ) for network traffice ?

Thank you