When Select Users: Choose Workflow Lookup for a User>While in the Selected Users:Double ClickWorkflow Lookup for a user>ChooseData Source:Current Item/Field from source:(The People Picker/Return filed as: Email Addresses,Semicolon Demlimited>ClickOK>Click*OK.
In the Infopath form set the people picker to allow multiple selections and I also did the same in the SharePoint list column for the people picker just in case.
I tried to upload a picture but it was taking too long.
The most important step was the [Return field as:] Email Addresses, Semicolon Demlimited.
I just did it before commenting on this and it work like a charm. I emailed up to 3 people with one people picker email workflow.
The logic is that you switch the data your pulling into emails and they fall in line with the Sharepoint Designer Workflow Email.
My name is Manni if you have any questions.
Have a great day and happy Solutions!