Yeah maybe they can't fuse because their gems are conjoined

They can't still fuse even if their gems are seperated that will cause a huge damage

Not to one of them one would be be missing an arm the other would be missing an arm and both legs (assuming they cant shapeshift limbs back

Hm

Yes they will be a Gem Shard

Of a head, chest and arm

?

A rutile twin loses an arm the other twin loses there legs and an arm

They might still be a shard but a shard of a head

(well a shard WITH a head)