Batting fifth or sixth is no different than earlier in the lineup. They would be reduced stress if they were batting in the number 8 and 9 slot.
If two runners get on in the first inning, and have not scored the pressure is on the 5 hitter if there are still runners on when 6 comes up, there is still pressure.
After the first inning the exact place in the lineup becomes less relevant. Without the 40-50 HR type ibatting cleanup, the cleaning crew falls to the next hitters