routing over vpn

I have a bunch of nodes on a remote network using RFC1918 private address
ranges. These remote nodes contain a dest IP value to allow them to direct
traffic at a specific listening service published on a static IP at my vpn
start point.

remote nodes
(10.10.10.0/24)
|
|
(192.168.10.1 )
remote router (vpn endpoint)
(99.99.99.99)
|
|
|
(80.80.80.80)
local router
(192.168.10.1)
|
|
|
(172.20.10.2)
vpn start point, ip sec adapter
listening service
window 2003

My problem is the remote router has commitments to other local ip ranges as
its managed by my ISP. The remote nodes dest IP value should be172.20.10.2.
I am trying to understand how my ISP can allow traffic from (10.10.10.0/24)
to route to 172.20.10.2. over an IPSEC vpn conneciton that i initiate.

What can my ISP do to make sure this traffic is routed to me ? , what do
they amend to enable this ?

Assume other users use 172.20.10.0 /24 range. What im trying say if customer
2 uses 172.20.10.0 /24 locally but 11.11.11.11/24 with the ISP is it
possible to allow us both to route to our own VPN start point ..... or is
this impossible to answer unless we know how the ISP nw is configured. But
even so , in theory is it possible ?

Thanks for any information
Scott