Dear Jane,
Thankyou for sharing your query with us. However, for us to work on this, please share the area of work for the employees, level, sector and the roles.
We can broadbase few 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 its evident that these employees are your billable talents, hence you may have a restriction on the number of days they would be avail for training.
Another area, that you may have to keep in mind is the Assessment. You have to plan, Pre and post training assessment with at least a 6 months view. It would be great if you can arrange for 1 year window.
Looking forward to hear from you.