Short answer: check the box to the left of Google Chat for your second Google Voice account (the one you configured on SP2, for fax.
Longer answer: I think you don't understand how this works. When someone calls your inbound Google Voice number, Google Voice will then simultaneously ring ALL check-marked 10-digit "linked" or "forwarding" telephone numbers*. Google Voice will also simultaneously forward those calls to "Google Chat" if check-marked. Think of Google Chat as a forwarding destination, just like 10-digit telephone numbers.
OBi devices can act as SIP "user agents" or clients for SIP VoIP telephone service providers. You set up one (and only one) SIP UA: SP3 for your inbound Callcentric telephone number. OBi devices can also act as Google Chat clients. You set up SP1 to act as a Chat client for GV account #1, and SP2 as a Chat client for GV account #2.
So: when someone calls your GV #1, it will ring your OBi SP3, because you have disabled Chat and enabled the CC number for that GV account. When someone calls your GV #2, it will ring your OBi SP2, because you only enabled Chat on that GV account.
*ring behavior is optionally altered by setting GV ring schedules and/or groups of numbers.