It primarily comes down to what you want, what your budget is, and how much load the websites are putting on the servers.
Generally speaking, a single Ryzen 7950X-based server can handle more than three E-2236 and will deliver faster page load times while handling more traffic. Since you are using three E-2236, you shouldn’t have any problem putting all of those sites into a single 7950X.
If you are after performance, and have a sufficient budget consider getting two such servers – each with at least two NVMe drives so you can set up RAID1. RAID1 will prevent data loss and keep the server running in the event one of the two drives fails.
If you need more redundancy than RAID, you will need to build an infra using clouds like AWS. It won’t be as affordable as getting one or two dedicated servers and will provide less than 50% (at best) performance in terms of page load times.
Also, consider LiteSpeed to further boost performance and offsite backup.