How to automate the process of creating and maintaining a network (less than 10) sites?

Question

Web development

Tell me how you can automate the process of creating and maintaining a network of sites.
The company has 8 sites from the "zero" sites for sales of various types of equipment. For each site - a separate direction. They do not want to pour all the sites into the category of one site.
The problem of maintenance is that one person is engaged in all sites. And the task from the management is to change "THIS" and "THIS" on site1.com, and as a rule, the change should be added to all sites, but there are exceptions. In fact, all 8 sites are similar to 98% (approximately), only the content is different.
So how to say I have a cry of the soul from everything I saw.