We would like to use D365 Marketing and Customer Insights but cannot get rid of our current CRMs. Is it possible to use D365 Marketing and Customer insights without using D365 Sales module?

We would like to use D365 Marketing and Customer Insights but cannot get rid of our current CRMs. Is it possible to use D365 Marketing and Customer insights without using D365 Sales module?
Yes. Dynamics 365 Customer Insights is actually a stand alone product which does not require any other Dynamics product to be owned. So, you can use it by itself, or with any of the Dynamics products.