Unfortunately, for now there isn't any option to put tasks parallel in one row due to inability of setting different height for each row. There are already similar threads regarding this functionality across forum: viewtopic.php?f=19&t=51280
In this thread you will find a simple workaround, which uses yAxis.breaks
and point graphic translation in order to allow expanding one rows' height and gathering points parallely. For applying the drag and drop functionality, it would require a further customization by e.g. overriding draggable-points
If you believe that such option should be included in Highcharts Gantt, you can post a feature request on GitHub repository: https://github.com/highcharts/highchart ... .md&title=
. The more people that upvote, the closer we are to seeing this idea become a reality.
https://api.highcharts.com/class-refere ... #translate
https://api.highcharts.com/class-refere ... xis#update
Let me know if you have any more questions!