I think a client can ping to other client or not depends upon your VPN type and its configuration. Regarding restricting the acces to other VPN clients following can be done:
1) You can use split tunneling and only network or host you want to provide access will be included in list .
2) You can give full access to that network and for certain application to block , you can use VPN filter OR
Configure ACL on inside interface to block return traffic to coming back.
Following link may help you
http://www.cisco.com/en/US/products/sw/secursw/ps2308/products_user_guide_chapter09186a00800bd983.html