I believe Lodin killed his co-conspirators for one simple reason. They had betrayed Prince Maxwell and Lodin was making damn sure that they didn't have the chance to betray him as well.

In regards to other Ventrue, I would suspect he would help sponser them to take praxis elsewhere. If there are busy fighting in other cities then there aren't going to give him any trouble. Any that are stupid enough to try will be quickly dispatched by his brood who have a tight grip on the city if they work together.

I have always pictured Lodin' brood to be completely dysfunctional...