Assuming you want to give up one GWS account and the O365 account: You would add the other two domains to your primary GWS account and add them as "secondary domains". This will give you three isolated GWS "instances" under the same GWS account.
Note that when I say "isolated" or "separate" it really means that each domain has its own set of users, but everything will still be combined under the same administration umbrella.
Read more about secondary domains and how they work here:
https://support.google.com/a/answer/7502379
Make sure you also read about the limitation when it comes to multiple domains under one account (see second paragraph, "Secondary Domains"):
https://support.google.com/a/answer/182081
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