(Haven't figured this out yet.)
can both be preceded by G.I.
are all types of ant
our second word is GIANT (which fits with the title, perhaps, since there the San Francisco Giants are a major league baseball team).
I'm drawing a blank on that first group. Mary Stuart and Malala Yousafzai were both "displaced persons", kinda; Malala Yousafzai and Theodore Roosevelt both had unsuccessful attempts made on their lives by shooting; all but Malala Yousafzai had spouses who died while they were fairly young; none of this seems likely to help. If there's any word that naturally goes before GIANT and fits the title, I've failed to think of it. (The baseball team isn't named for any feature of SF; they were the New York Giants before they were the San Francisco Giants.) They've all been characters in movies, but that doesn't seem like a special enough characteristic.
Note: Let the record show (as the timestamps may not always) that Matthew Barber's answer with the same answer to the third group was posted before this one. (But, also for the record, I got it independently.)