Adding a person for 4 nights how do it affect everything

My son is coming down with us for 4 days of our 8 day trip. Do I have to pay extra for the hotel room, he is considered an adult, so it would be 3 adults in the room.
Also how does that affect our Magic Bands/Fastpasses. Does it?

Do you have a room only or a package? What resort? A 3rd adult is an extra fee per night. That fee depends on the resort level.

Pop Century room only

If you want him to use ME or have a magic band then yes - you would have to pay the extra adult charge.

Last year, my sister came for three of six nights. We had to add her for the full six nights, but I went to the front desk (on advice from my travel agent) and they refunded me the extra adult charge for the nights that she was not there.

You can try to add a person to your fastpasses or just look for one in that time frame. It shouldn’t affect your existing magic bands or fastpasses.

I would add him. You can identify on DME that he is arriving separately . If he is over 18 then then is the nightly fee but for value I believe it is about $15?

Sounds great, thank you,