You would not be on two DMDs at the same time, especially not with
Tysabri. Previous DMD use has to be stopped
and there is a washout period of at least 30 days before you can begin Tysabri. If the neurologist doesn't require a washout period, get out of there and go to someone who knows what they are doing.
If you choose to go off of Tysabri, there is going to be another washout period. The recommended length for Tysabri to gilenya, is about 4 months.