Do you want two SSL certificates for one domain or IP address? Of course, you can have them. There are no rules, whatsoever, to stop you from having 2 SSL certificates for one domain.
There are a variety of reasons why you may want to use two SSL certificates for one domain or IP address. For example, you may choose to install a second SSL certificate to ensure that your site and services don’t experience downtime because your existing certificate will soon expire. Or, you may have one domain hosted on multiple servers and may be using a load balancer.