Wasps second row Launchbury has pulled out due to injury, with a fibia stress fracture causing him issues, and Harlequins prop Marler has withdrawn for personal reasons.
Bath’s Charlie Ewels and Wasps’ Tom West will join the squad ahead of the Six Nations, which begins on February 6.
The call-up is a first one for prop West and he will meet up with the rest of the squad at St. George’s Park on Wednesday.
West will take Marler’s place in the squad, who tweeted on Monday afternoon to explain why he has withdrawn.
“Always grateful for the opportunity so not an easy decision, but want to do right by my family in these crazy times and won’t be meeting up with the squad for this tournament,” he tweeteed.
"Look forward to watching the team rip in. Go well.”