I think you would need to create 3 associations between A and B (all *-1).
Do you need to store a value in Col1 on entity A? or is it sufficient to show the associated value from B?
If it is enough to show, you don't even need Col1, because you will show the value from the string attribute on B on your form.
If you need to store it, you can use an on change microflow that copies the value from B to col1. And do the same for the other columns as well.
Hope this helps.