I remember a lot of controversies around gore in brickfilms. I think forrestfire101's Lego Captain America series caught a lot of flak for its gore and violence, back when it came out.
It's not hard to imagine why people would be opposed to it - LEGO has traditionally been focused on young people. Something like a sword fight wouldn't necessarily be too violent, cutting off people's heads and blood spurting everywhere gives it a different tone. I think LEGO (and brickfilming as a medium) has matured a lot in recent years, though. I feel like a lot of people have moved on past the idea that LEGO is a toy so anything related must be cartoony and kid-friendly.
Having said that, you may want to think about how you use gore in your films. You say you want to focus on brickfilms that are comedic. In that case, is the gore really necessary? Could a film (or joke) do without? I'm not saying to avoid gore outright: most Tarantino films are proof that gore/violent content and comedy can go together quite well.
I think it's still mainly younger kids who are interested in watching brickfilms. If you're planning to focus on a slightly older audience (PG-13, or >12 year old as you say) I would suggest making sure that viewers know this before they are exposed to the gore. You could put a warning at the start of your film, or even put something like (PG-13) in the title. YouTube is in the midst of policy changes to (potentially) kid-friendly content, so make sure your videos (and perhaps your whole channel) are set to not made for kids! This will also help protect younger kids from accidentally stumbling upon your content.
Anyways, that's my two cents.
