@Suzanne802 from your post is not clear if you booked for 2 people or just for yourself.
Does this place accommodate just 1 or 2 guests?
Is the same price the same for 2 guests or the second guest is additionally charged?
If this place accommodates 2 guests and you booked for 2 then an extra blanket shouldn't be a problem .....but if you booked for 1 and now you are asking for another set of bedding (it's not just a blanket, he has to prepare sheets and pillow as well) and if your host is out of town or he doesn't have an extra set of bedding bc he can accommodate just 1 guest at the time, or he has to pay a cleaner to come again and prepare another bed for your brother.....then the only thing you can do is to cancel or to ask your host if you can pay extra for your brother.
Responding to messages within 24 hours is a good practice but not everyone has a mobile phone application and notifications so sometimes messages are not seen and answered timely. It happens quite often that my guests don't answer my messages for weeks and until the day of check-in
As others have said - extra guests and services should be communicated BEFORE booking through a link "contact host"