Sounds like you got confused by the "5's" or "5's and 6's" associated with the 365 Family subscription.
365 Family can be "shared" by the subscriber with up to 5 (formerly was only 4 shares (4+1makes 5) family)
365 Family / Personal can be installed on up to 5 computers at the same time by each licensee.
So 365 Family used to be "5&5" and now is "5&5+1" or "5&6". Users often get confused by all of these 5's and 6's ...
Do you need all 10 devices to be signed in to Office at the same time? (what are you, a "Siameese Twin" octopus that you can use 10 devices at the same time ... ? <G> )
If you don't need more than 5 active at the same time, you can let Office "play musical chairs" with the devices. When you need a device that is currently not active, just click on the "Install" button and MS will transfer one of your active counts to the current device. It doesn't actually install the program (again), it just assigns one of the activation counts to the new device, removing it from the least recently used device.
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You can save money 2 possible ways. If you have not "used up" your 5 (actually 10 between the 2 subscriptions) shares on the Family subscription(s), you could share with yourself, by sharing from your "primary" email to the "secondary" email you used for the second 365 subscription
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If you don't want to share with yourself for some reason, and you don't share with anyone else, you could go with 2 365 Personal subscriptions. Slightly more expensive than 1 365 Family, but cheaper than 2 Family subscriptions that you are not using to share.
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PS: as an observation, if you have 10 devices signed in to at the same time, it sounds like maybe you are using them in a "school", ie to train people in a classroom setting. Sorry to rain on your parade, but 365 Family is not licensed for this type of use. In that situation, ideally, you should be paying for 10 business 365 subscriptions, but you could cheat and only use 2 subscriptions (I didn't tell you that, we are not allowed to make that sort of advise).
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