Total utilitarianism is defined as maximising the sum of everyone's individual utility function.

That seems misleading. Most of the time "total utiltiarianism" refers to what should actually be called "hedonistic total utilitarianism". And what is maximized there is the suprlus of happiness over suffering (positive hedonic states over negative ones), which isn't necessarily synonymous with individual utility functions.

There are three different parameters for the various kinds of utilitarianism: It can either be total or average or prior-existence. Then it can be negative or classical (and in theory also "positive", even though that would be insane, forcing people to accept eternal torture if there's even the slightest chance of a moment of happiness). And then utiltiarianism can also be hedonistic or preference. Most common, and subject to this article, is (classical) total hedonistic utiltiarianism. While some combinations make very little sense, a lot of them actually have advocates. (For instance, recently someone published a paper advocating "negative average preference-utilitarianism".)