Consider the sentence, "I have 4 brothers and sisters."

Does that mean the person has 4 brothers and 4 sisters or does it mean the total number of siblings totals 4

I would take that to mean 4 siblings. 4 of each type I would say (and expect to hear) "I have 4 brothers and 4 sisters"

It is four all together.

If you put a quantifying adjective in front of brothers (4), you would have to put one in front of sisters to make it sound correct.

You wouldn't say, "I have motorcycles and cars." You would say, "I have a few motorcycles and cars." or "I have some motorcycles and cars."

In spoken English, if you are going to tell us that you have multiple objects, you might as well tell us how many.

It means four siblings altogether. You would say "I have four brothers and four sisters" if that's what you meant.