Yes you can. You will be asked if you want to apply for either one or both ensembles when you complete the application form. Some instruments are only accepted in one ensemble, so in that case you only apply for that one, but otherwise you can apply to both or just one. If you apply to both you will be asked if you have a preference or not. Some instruments (in particular flutes and clarinets), do have  a lot of applications so you may wish to apply to both to widen your opportunity to gain a place.