Once created each NFT has it’s own wallet which is part of the block chain and cannot be deleted.
You can edit the extra NFT wallets (the two with zero plots) out of your config.yaml under the pool_wallet heading if I remember correctly. The wallets will still exist but your Client will not know about them.
The limit of 20 wallets includes your main wallet leaving only 19 for multiple NFTs and their wallets. KeyBase suggests you create no more than 18 NFTs and I suggest you never get near that many, lolz!
Fortunately, your extra NFTs contain no plots. Once removed from config.yaml zero plot NFTs added are no longer a problem.