Incorrect relative added - now an entire incorrect branch exists

I added a person who I had been told was my father, and then added relatives dating back to the 1600s.

Now I know that data is incorrect, but I can't delete the people I added because they're "connected to" someone else, and I'm told I have to delete the other connected person first, which I can't do because they're connected to others who are connected to others who are connected to trees I don't have permission to be making changes on.

So I started just edit the names of the people in my tree to put in the correct names, but now these people appear as descendants of the incorrect ancestors that go further back.

I either need to break off a branch, or delete the entire thing and start over, which I'm willing to do because it will take minutes to rebuild, whereas I've wasted hours trying to fix this.

There needs to be a way to make corrections, or break a connection to someone who doesn't belong in the tree. When trying to fix some inconsistencies, I get a warning that this will split the tree. That would be freakin' great if I could split the tree and no longer have non-relatives in it!  But it greys out the button and won't let me remove the poeple I need to remove.