Thanks for building on Twitter. For a general refresher on Twitter policy as it relates to spam we suggest that you review the Automation Rules and the Twitter Rules.
Also, per our recent blog post we can confirm that posting identical or substantially similar content to multiple accounts is not permitted.
Do not (and do not allow your users to) simultaneously post identical or substantially similar content to multiple accounts. For example, your service should not permit a user to select several accounts they control from which to publish a given Tweet.
This applies regardless of whether the Tweets are published to Twitter at the same time, or are scheduled/queued for future publication.
As an alternative to posting identical content, you can Retweet content from one account from the other accounts you wish to share that post from. This should only be done from a small number of distinct accounts that you directly control. Please note that bulk, aggressive, or very high-volume automated Retweeting is not permitted under the Automation Rules, and may be subject to enforcement actions.