thank you for your answer
I wish I could explain it better but english is not my first language so I get confused and don't want to confuse you
but the basic is that she clicks 'alt' to link the layers and the brush painting only affect those 2 layers linked, so she can paint the curves (smart vector/tracing) in a new layer that is linked with the curves, when I create a new layer and group with the curves or the layer that I want to paint on photo it paints everything and not only the two selected layers.
I wish I could show you the tutorial but it's not in a free plataform so I don't think it's legal, but it's not group the layers, she wants to change the colors of two elements in a safe way, she creates a new layer above the one she wants to affect and clicks Alt and then she uses the brushes in that one new layer and she does the same thing in the curves.
Like in the print screen, the 'Layer 21' is linked to 'FLOR 3' (she clicked Alt)
the other example:
the final result is this:
too confusing?