No, there is not a way to do that. If you want them to be able to opt in to more than one newsletter they have to have the checkboxes so the user can decide which ones he wants to opt into. It should be clear to the user if he is opting in to more than one newsletter, otherwise if he later unsubscribes to one of them he will think you are spamming him when he continues getting the other newsletters.

it depends, if the user is registered on the site they can manage their subscriptions from their profile. But non members can only unsubscribe from  the newsletter unsubscribe link. Administrators can also unsubscribe anyone.