I'm not familiar with Darius Twin for SNES, but why don't you try the games for yourself?
Start with one version of Darius II (the previous game in the series), and one version of Darius Gaiden (the following game): either or both should have direct relationships.
Then try the first Darius (presumably close to Darius II), then other clones of all of the above because they could be a bit different, and maybe, if you don't smell of fish yet, the newer G-Darius and G-Darius ver. 2 for completeness.
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