your description and your image are not same.,I'm not sure what you meaning.
I can't replicate follow your issue description (*After reservation successfully,It is sending email double* )
I just fixed follow issue image (*email display wrong*) by add code for fix when found thank you email template not match version
In the future, if there are issues around this. please call technical team (K'Vut,K'key) for compare email template between B2B and Backend before.