We have gotten to the size that we are having problems managing password for our clients and staff.
We have multiple staff that work on multiple sites with multiple passwords. How does a MSP with 10 employees and 100+ clients manage passwords?
How do you manage Google office without having to buy a extra account for each customer. We buy a management account but only use it to manage the account. We do not use the storage or other services.
I’d say the best approach is to manage clients and not passwords !
A wiki site is surprisingly useful in this regard.
We use https://bitwarden.com/ enterprise for password management.
There is not an official way to do it from google that I am aware of, but it can be done… (of note you need to do manual licence assignment once you set this up)
And surprisingly insecure, too 
As Tom suggested, Bitwarden is a good option. I would throw 1Password in the ring as well. While it’s a paid product, it’s also one of the best, especially in a business environment. Their security architecture is incredibly good, too.
You have multiple options here:
1.) Become a Google partner, e.g. reseller. As a partner, you can access all your customers’ admin consoles and manage their environment without having to add additional admin users. It also gives you a nice cut of the revenue (20-30%).
2.) if number 1 is not an option, you can enable “Cloud Identity Free” subscriptions to all your customers. This allows you to add free licenses for users like admin users (they can’t use any of the Workspace products, but they can use the admin console). Here is some more detail on that:
https://cyrrus.cloud/blog/how-to-save-money-on-google-workspace-licenses
we have implemented HashoCorp Vault, and I should say during last months, it’s kinda a game changer.
I’d advise to get a closer look for this product.
Keeper MSP for credential management here, Can link to entries to it from our Wiki.