Do I want a multisite?


I have added my site I also own 2 other domains (; and that are meant to be connected to my main site, as one is a sub-brand and the other is my brands blogsite. I want them to be separate where they have their own logos at the top of the site etc but using the same system. For example has and connected. But separate. I want customers to be able to sign up for one site and be members for the others as well. I want them to shop at and add items from to the same cart. Is this possible? What is the best way to do this?