Is there a blogging option that won't take over my whole site?

Is there a blogging option that won't take over my whole site?

I have an exsisting site that serves a community of performers that puts
on shows. The site has a variety of features and functions to display
schedules, maps, show information, performer profiles, and so on. All of
it built from scratch using PHP, MySQL, and some Javascript.
We'd like to include a blog that has the ability to upload sets of
pictures and display them as galleries, embed videos, and have multiple
people contribute.
The problem is that, as the person who develops and maintains this site, I
feel trapped between two worlds. On the one hand, developing all that code
for a blog that acheives all that is a lot of work, and, my experience is
that in the end it's hard to handle everyone's opinions on how the
interface works and what features are available. On the other hand, trying
to use existing blog services with robust features, like Wordpress, means
I have to give up the whole site to the blog system, and I have to
reinvent the wheel to get features I've already built, and take both
myself and my users on a whole new learning curve just to get to where we
largely were before anyway.
What I'd really like is a set of code for handling blogs that doesn't take
over the whole of the site, but is robust in handling blog related
activities.
Does such a blogging system exist? Something that handles blogging but
works within an existing layout?
(I almost thought hacking Wordpress to display in my existing site layout
would work, but it's proven to be problematic in that it basically amounts
to having a whole site within a site)