Your last sentence shows that you know what's truly important. You want to be there to support your friend who lost their son. That's all that really matters.
Funerals can be awkward; I haven't been to many that weren't, in one way or another. They often bring together a group of people who have issues with &/or feel uncomfortable about some of the others there. However, this is common, so I'm fairly sure your other co-workers will have been raised to know how to behave politely in this situation. If not, they'll be the ones looking weird ~ as long as you keep it pleasant and neutral. Which shouldn't be too difficult, as, in most cultures, it would be improper to show any negative feelings about other funeral attendees during the event. Which everyone knows, so they won't be attacking you in any way, due to the cultural agreement that at a funeral it's just, you know, a little smile, nod, look away, move on. Mumble a little something if need be.
Anyone who acts like a jerk to another person at a funeral is really going to appear very rude themselves.