Double-single tracks
Personally I always use single track, but that's just my preference. In all the track I have laid, 13 routes on the Ds. no single rail reversed when a spline point was added, that puzzles me why it should.
To use a double junction with double straight (ish, ha, ha) track first put a spline point in the double track. Then you can add a single to each spline point and you have a junction. Be sure there is a lever on each join.
On double track and as stated, they are both in the same 'direction', that is the built-in directions go the same way. When you place a train on the line that is 'wrong' you must reverse the drive direction and heading on the train, then it will run against the grain, so to speak. But just to be sure use Direction Markers on that track to ensure your trains run in the direction you want.
Whatever you do the AI and Alistair will find some way of not doing it, that's certain!
Angela