Kinda not very good config if you have only 12 drives .... but i would not suggest to YOU to reinstall system ....
Are those aggregates raid-dp or raid-4? Do you have spares for each controller?
I would configure 12 drives as:
1) contr1 - 3 drives = raid-4 + hs (1 aggregate and 1 volume (root))
2) contr2 - 9 drives = raid-dp + hs (1 aggregate and 2 volumes (root, data)) -> ~ 6x 1.62TB and deduct some for root volume
No, you cannot reconfigure without reinstall.
Write down somewhere all licence keys from both controllers .... just in case
I hope your question about size and raid options is answered? 😉