Before I get into dismantling the rest of this post let me first deal with your the part of your post that is actually related to the topic. You said
"It appears to me that the parable was quite finished when Jesus stated to bring his enemies before him and to slay them.
The parable ended in Luke 19:25.
During the parable, there were many statements such as "and he said .. ." which indicate that it is part of the parable.
And then in 19:26 Jesus says, "And I say unto you . . . " Now Jesus is talking to the audience. The parable is over.
So, when Jesus commands to bring forth his enemies and slay them, that is no longer part of the parable, but a command of Jesus himself."
But let's look at the verses preceding it...
Luk 19:23 Wherefore then gavest not thou my money into the bank, that at my coming I might have required mine own with usury?
Luk 19:24 And he said unto them that stood by, Take from him the pound, and give [it] to him that hath ten pounds.
Luk 19:25 (And they said unto him, Lord, he hath ten pounds.)
Luk 19:26 For I say unto you, That unto every one which hath shall be given; and from him that hath not, even that he hath shall be taken away from him.
Luk 19:27 But those mine enemies, which would not that I should reign over them, bring hither, and slay [them] before me.
The people in the parable were still talking to the Lord of the parable and verse 26 along with 27 were the parable Lord's response. It flows more evenly if you leave verse 26 out as some versions do. Either way it is appearant to anyone being honest about the passage this was part of the parable. The greatest indicator that this wasn't a command however is the fact that the disciples didn't start rounding up anyone for slaughter. Guess you didn't notice that. Perhaps if you devoted time to an honest reading of the Gospels you wouldn't need to depend on these out of context quotes to support your thesis.
I will reply to the rest in the coming days as time is short for me at the moment, but I wanted to address that first.