Certificates are bound to a hostname (or wildcard hostname), so you’re fine using the same cert on multiple machines.
However, when requesting a certificate, you usually create a private key on one of the servers. This private key needs to be copied to all machines in addition to the actual certificate that you receive.
One scenario is where you have www.domain.example resolving to an IP of a load-balancer, which in turn forwards the traffic to multiple servers. In that case, you only need a certificate for www.domain.example that you copy (with the private key) to all servers in your cluster.