Thank you for sharing your query with us. However, for us to work on this, please share the area of work for the employees, their level, sector, and roles. We can provide a few broad suggestions for you. Help us fine-tune them with the background of the need for training, any budget that you have, and the resources that you can put in. Since it's evident that these employees are your billable talents, you may have a restriction on the number of days they would be available for training.
Another area that you may have to keep in mind is the assessment. You have to plan pre- and post-training assessments with at least a 6-month view. It would be great if you could arrange for a 1-year window. Looking forward to hearing from you.
Regards