Can the members of the group still be checked out individually?
Assuming that your answer is yes, you can add records to your Assets table that identify a group of assets. This is often called a "kit" and is also called a "package deal" in some invoicing systems.
Assets::__pkAssetID = Asset_Group::_fkGroupID
Assets|GroupMembers::__pkAssetID = Asset_Group::_fkMemberID
Assets and assets|GroupMembers are the names of two table occurrences based on the same table.
You can use a portal to Asset_Group on an Assets layout to build a a list of assets as a member of that group. Note that it is possible with this set up to assign the same asset to more than one group though there are ways to prevent that if it is undesirable
Checking out an Asset to an individual usually means creating a new record with the asset ID and also the ID of the person checking out the Asset. A script trigger can be set up on that layout such that each time you add a new asset to the list, the script checks to see if the selected asset is a group asset. If it is, it uses the list of ID's in Asset Group to add all of the group members to your list of assets checked out to that individual.