Canceling marketplace insurance to go on Medicare

I have a marketplace plan for myself and spouse. I begin Medicare on July 1st but spouse begins later in year. It is my understanding that I call the marketplace to cancel my coverage the end of this month and that my spouse will stay on the same plan and may have to sign back up again. Is this correct about having to sign back up again and if yes, will all deductibles met that have been met for the year stay the same since it will be the same plan? It seems it will be cutting it close to pay the marketplace premium if everything is done the final day of the month. Thanks for any input