i want a solution in vpn site to site from my company to another company (100D fortigate)

hi all

i had tried to do site to site VPN from HQ to Branch and the connection is good and still going on.. but i never tried to do VPN site to site between different company's ... i want to do it with out full connection between us...

for example i don't want them to do ping to my wan interface .. 

the other company give us a Excel  file with all connection information ( phase 1 , 2 )

and also give us a local ip address but i don't know how to deal with it

please for give me because i am a new in fortigate firewalls