A Nintendo Switch Online Individual Membership cannot be transferred to a different Nintendo Account. If you want to cancel your membership, you can turn off the auto-renewal setting to discontinue the service at the end of your current term. (Make sure to turn off auto-renewal at least 48 hours before your membership is set to expire.)
A Nintendo Switch Online Family Membership can include up to 8 members. If you would like to add additional Nintendo Accounts to a family membership, the family group admin can add the accounts (up to 8 total) to the family group. Everyone in the family group will be able to use the service.