Adding a Person to Seaside - Options or Suggestions?

We are booked on the Seaside next year for cabin 9002, which looks like a promising room. We are a party of two adults and two kids. My brother has shown an interest in going. When I do dummy bookings, we can move to a whirlpool suite for the 5 of us for about $2,000 more than our current booking. This would also include an upgrade to Aurea, and a whirlpool tub on the balcony! When I look at booking an additional balcony cabin for two it is $2,099 for Bella class. There is no one that he can think of to take with us to share his suite or that he would want to split a room with. I tried to put in for one person, but it gives me no selections when I do this.

So, do we chance it and book a different room or should we get a second room and keep 9002? After reading some of the experiences recently with customer service I'm not really looking forward to contacting them to try to switch rooms.

Any other options that I can't see or pros/cons to the choices above? Thanks in advance!