I have side mounted wheels on my tadpole trike, and to take into consideration the side loading when cornering, they have 14mm BMX axles.
The side loading may not be as much of an issue for the Halfway, as you can lean into bends. I suspect the axle to be a proprietary type and more beefed up than standard axles, at least at the attachment end.
Perhaps not a good starting point for modding ambitions.