The singular is includes. (He includes me in everything.) The plural is include.

Is it this includes or these includes?

Several different users can change their own passwords; these include administrators, and normal users. The "these include" refers to "several different users." But: ... In this case, the "this includes" is singular, because it refers to the single principle that no user is allowed to change a password.

Which includes or that includes grammar?

The battle over whether to use which or that is one many people struggle to get right. It's a popular grammar question and most folks want a quick rule of thumb so they can get it right. ... If the sentence doesn't need the clause that the word in question is connecting, use which. If it does, use that.