SURE! The workbooks are not a necessary component,  as they are not intended to "track" with the Whole Family Spanish. They have a simple list for each week, the audio included, and straightforward exercises leading the family through the easy lessons.  SiSi has everything you need (other than a set of blank index cards.) The workbooks do teach different content (mostly - there is a little over lap) in a different way, and this switch up often invigorates the child who likes to doodle and draw, and add on more conversational Spanish.  I usually recommend that the family choose one method, and then switch it up after three or four months, if you desire to have both methods. Hope that helps! There's a note about this on the workbook pages, and I think it's more in depth.