Tried your link. Results:
yum install /tmp/FirebirdSS-2.5.9.rpm
Loaded plugins: fastestmirror
Examining /tmp/FirebirdSS-2.5.9.rpm: FirebirdSS-22.214.171.124139-0.amd64
Cannot add package /tmp/FirebirdSS-2.5.9.rpm to transaction. Not a compatible architecture: amd64
Error: Nothing to do
Kernel and CPU Linux 3.10.0-1062.18.1.el7.x86_64 on x86_64
Looks like their packages are bad at this point. You definitely have the right, matching architecture there. Seems that they are having a lot of problems these days. It's such a niche product, I'd be super wary of every using it in production or any software the depends on it. Using it as an option, sure, but requiring it I'd consider a non-starter. Absolutely no one supports it.