Explanation
Two considerations when installing a managed package in a sandbox are:
The installation link has to be modified to test.salesforce.com, because the default installation link points to login.salesforce.com which is for production orgs. To install a package in a sandbox org, the administrator has to replace login with test in the installation URL before clicking it.
The package will be removed any time the sandbox is refreshed, because refreshing a sandbox replaces its current data and metadata with those from its source org. If the source org does not have the package installed, then the sandbox will lose it after refresh. Any metadata changes to the package do not have to be recreated in production, because they are preserved during upgrades unless overwritten by the package developer. Install for Admins Only is not the only install option available; there are also Install for All Users and Install for Specific Profiles options. References:
https://help.salesforce.com/s/articleView?id=sf.distribution_installing_packages.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.data_sandbox_implementation_tips.htm&type=5

Explanation
Splits is a feature that should be used to meet this requirement. Splits allows users to assign credit to opportunity team members based on the level of effort contributed by each person toward each deal. Users can createdifferent types of splits, such as revenue or overlay splits, and specify the percentage or amount of credit for each team member.
References:https://help.salesforce.com/s/articleView?id=sf.forecasts3_splits_overview.htm&type=5

Explanation
Process Builder is an automation tool that allows you to create processes that perform actions based on criteria that you specify. You can use Process Builder to update fields on related records when a record is created or updated. To meet the requirement of updating the parent object Referral when the Referral Date field is updated on the custom object Referral Source, you need to create a process that triggers when a Referral Source record is updated, checks if the Referral Date field has changed, and updates the Referral Date field on the related Referral record.
References:https://help.salesforce.com/s/articleView?id=sf.process_overview.htm&type=5