All of these garments are at the Monasterío de Santa María la Real de Huelgas, Burgos, Patrimonio Nacional

Go here for Marc Carlson's drawings of these garments.

Go here for Maura Folsom's drawings of these garments.

Leonor's saya and pellote

Close inspection at the museum shows that there is a "tape" attached to the underside of the opening.
This is fastened down at regular intervals, and through this the laces are threaded.

Fernando's pellote