Parent company with many locations vs subsidiary with fewer locations

I’m working for a parent company that has 5 smaller companies under it. The parent companies website will have all 100 or so locations. The smaller companies websites will only have about 20 or so locations each.

Should I create the parent companies website first, with all of the locations? Then, when making a map for a smaller company, copy that map and delete all of the locations that arent for the smaller company?

And if so, can I do all of this with only one API key for both the parent company and all of the smaller ones?

Thank you for any suggestions.

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