Nevermind, figured it out! I'm sure there's other ways but here's what I ended up doing in case anyone else finds it useful:
Select Top 1000000 tblO365Group.DisplayName As [Group Name],
tblO365User.DisplayName As [User],
tblAssets.AssetName,
tblAssets.Lastseen,
tblAssets.AssetID
From tblO365Group
Inner Join tblO365GroupMember On tblO365Group.GroupId =
tblO365GroupMember.GroupId
Inner Join tblO365User On tblO365GroupMember.UserId = tblO365User.UserId
Inner Join tblADusers On tblO365User.UserPrincipalName = tblADusers.UPN
Inner Join tblAssetUserRelations On tblADusers.Username =
tblAssetUserRelations.Username
Inner Join tblAssets On tblAssets.AssetID = tblAssetUserRelations.AssetID
Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
Where tblO365Group.DisplayName = '<YOUR O365 GROUP NAME>' And
tblAssetUserRelations.Type = 1
NOTE: tblAssetUserRelations.Type = 1 by default is "Owned By". If you don't have relationships setup you can leave this out.