Can apps use different Twitter accounts on iOS?
Developers access your Twitter accounts through the Accounts framework.

When an app requests access to your accounts, it uses the requestAccessToAccountsWithType:withCompletionHandler: method. (The only supported account type is currently ACAccountTypeIdentifierTwitter.) This grants access to all accounts of that type.

Therefore, unfortunately, apps can't request access to only a single account — you have to give access to all of your Twitter accounts.