Load-bearing capacity for floor joists

[Knecke]

Hi guys, you're talking about things I don't understand at all but my question still remains =)

However, I think we'll put up a beam in any case on this stretch since we might intend to make the bathroom upstairs larger in the future, and it feels a bit troublesome to have to deal with it afterward downstairs.
The question is just what size the beam needs to be. The stretch it will sit on is 3 meters.

 

[Knecke]

I have taken down a bit of the ceiling to get a better look at how it is structured. It turns out that the joists do not extend from outer wall to outer wall but rather from the outer wall to the heart wall and then a new beam continues from the heart wall to the next outer wall. However, there are 3" 8" beams in place anyway. Is the load-bearing capacity negatively affected much by this? The distance is still about 4.3-4.5 meters.