If you peer VPC A to VPC B and I peer VPC B to VPC C, does that mean VPCs A and C are peered?
No. Transitive peering relationships are not supported.

http://www.interviewquestionspdf.com/2017/01/if-you-peer-vpc-to-vpc-b-and-i-peer-vpc.html
No. Transitive peering relationships are not supported.