"Maria's, Mary's and Sophia's first loves was Katarina.
"Katarina was Maria's, Mary's and Sophia's first loves"
"The first love of Maria's, Mary's and Sophia's was Katarina."
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Sign up to join this community"Maria's, Mary's and Sophia's first loves was Katarina.
"Katarina was Maria's, Mary's and Sophia's first loves"
"The first love of Maria's, Mary's and Sophia's was Katarina."
I'd go for the second statement in your list but with a correction - "Katarina was Maria's, Mary's and Sophia's first love."
It looks simpler than the rest.
The first sentence also looks fine, but again with the small correction - "Maria's, Mary's and Sophia's first love was Katarina.
The last sentence would be my last preference.
Although, I should add that the order of preference will vary depending on what you're trying to emphasize.
Hope this helps.
NS