In situations where I have a Lambda processing events from DynamoDB that need to trigger multiple other Lambda I find the best solution is to publish a generic message to SNS then use the fan out functionality by configuring multiple Lambda as subscribers (just add the same topic as a trigger to each Lambda).
For example: When a new user is added to DynamoDB you could publish a “created” message to the “user” topic then subscribe two Lambda to the user topic (one to send a welcome message and one to add the user to a mailing list)