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Are any of your BM's OOT? If so, I agree with VicTim328... they have to be able to get it home on a flight or across state lines potentially.
What kind of budget do you have? Are there specific shared interests they all have? What are their favorite hobbies, interests? Do you want to get them all the same exact thing, something similar, or each BM something unique to them?
If you're looking to keep things the same or similar than try to find a common interest to come up with a gift. If you're ok with entirely different, try to find something specific to them and their interests.
I think people might be able to offer you more constructive ideas with a just a few more details.