This is illegal by rule 3.4.2. — Rule 3-4-2 states that a person must not move over or be under a partner stunt or pyramid except when helping build, stabilize or dismount that partner stunt or pyramid. (page 24) Because the two team members would be considered bases as they lift and become weight bearing then this would be a partner stunt by definition. See the definition of ‘base’ on page 9 and ‘stunt/partner stunt/lift’ on page 12. This stunt meets the definitions for both ‘base’ and ‘stunt or lift’.
It’s further illegal by rule 3.8.1, as you can’t tumble under a stunt. (p 31)