Hi Carl,
siteA = subnetA; siteB=subnetB...
you need to modify your proxy ACLs: (crypto map outside_map 10 match address ACL_NAME)
On siteA right now vpn = subnet A to subnet B; add subnet A to subnet C
On siteB right now vpn1 = subnet B to subnet A and vpn2 = subnet B to subnet C
add the following:
vpn1 add subnet C to subnet A
vpn2 add subnet A to subnet C
global config add same-security-interface permit intra-interface
On siteC right now vpn = subnet C to subnet B; add subnet subnet C to subnet A
Also fix the NATs and interface ACLs accordingly...
Hope that helps,
Patrick