Will the accessories from the Define R6 fit the Define 7/XL or Meshify 2/XL?

Yes

• SSD Bracket Kit - Type A
• Flex VRC - 25

No

• Define R6 Tempered Glass Side Panel
• Connect D1

Kinda

• HDD Tray Kit - Type A
  • The Type-A kits from the Define R6 are not technically compatible with the Define 7/XL or Meshify 2/XL. The Type-A kits have a plastic piece on them that allowed them to be mounted to the R6 whereas the Type-B kits have a small metal flange. (Example shown below)
    
    
    However, if you're in a pinch you can make the Type-A kits work for the Define 7/XL or Meshify 2/XL by removing those plastic pieces. The only thing is that the trays then have to be secured by the optional mounting screw since there is not a metal flange on the Type-A kits as there are on the Type-B kits. Also, if you are installing the Type-A kits into the Hard Drive Cage Kit Type-B accessory then you wouldn't have any issues.