When Company downsizing their team especially sales, what the best scenario to eliminate negative impact on business?

Making staff redundant is guaranteed to have a negative impact on morale: don't pretend or hope otherwise.

There is going to be a negative impact on the business because you have fewer sales staff, which is very likely to reduce sales.  Again, don't imagine otherwise.

Most businesses do not let enough people go at first.  This means there has to be another round of redundancies, and morale falls further.  Fewer sales staff with lower morale means lower sales ... which leads to more reduncancies.   The company is them embarking on 'death by a thousand cuts'. 

The best technique is to get it over with in one blow, if you can, and make sure you lose the staff you can afford to lose.  Your good people will start jobhunting the next day, so give them a reason to stay.