You will not be able to get the order that you want.
you are first ordering events by start event_start' => 'DESC',
then by end 'event_end' => 'DESC',
the following two orderby values will have not effect because you are trying to order by the same values that have already been used to order the values.
1 and 2 are not an issue, but placing past events after upcoming events will be impossible using WP_Query.
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