This would produce like this parallel splines according to offset I added in scripts Y
Result
So when it comes to actually 1:1 being parallel what you mean can be different as mentioned before.
In your example of the pink, its an offset to the curve itself meaning the length and the points positions are not the same anymore. Its like white is the road, and pink is the pavement following the road, yes they are parallel however turns and curves tangents are not the same anymore they are adjusted. If you want to do that (scaling) simply.
This would simply segment the spline and recreate many points but true parallel as you ask. The points on the target will not be matching the spline original interms of number however shape direction wise it will be very accurate, till your turns are bigger than the offset then as nature it should be clamped.
Results
https://dev.epicgames.com/community/snippets/gRbE/unreal-engine-parallel-spline-replication
If you want also after the construction and points created you can add additional tangents if you like
This will auto adjust proper tangents.