A .sea file AFAIK is a basically a StuffIt-compressed archive with the expander built in. It is a Self-Extracting Archive so should expand when you double-click on it, though this will require Classic if you run OS X. It should still show up as an application. If it doens't, it's most likely damaged, although StuffIt Expander might still be able to expand it.
A .dmg file is a disk image. That's a whole different kettle of fish. You're not going to be able to 'convert' from a compressed archive to a disk image - you can obviously make a disk image, expand the archive and copy the files to the disk image, but convert? No.
At least, that's unless I'm completely misunderstanding your answer - and I must admit I'm likely to be, since I don't have a clue what Sweet16 is and why it needs to like the .sea files.