From B2evolution

Some users may want to present multiple, separate blogs together on one page. The multiblogs.php file is a proof-of-concept file which will display 3 blogs of your choosing at the same time. You can see an example on the demo site: http://demo.b2evolution.net/HEAD.php4/blogs/multiblogs.php.

By editing the multiblogs.php file you can set which blogs you wish to display in which order. Blogs are chosen by their database ID numbers. You can find the ID number for a particular blog by looking in the backoffice under the Blogs tab. Roll your mouse over any of the blog names you have created and in the URL you will see "blog=1" or "blog=12". That is the ID you would need for multiblogs.php.