There is currently no feature for bulk deletion.
With Premium Pro, you can download multiple photos and videos at once. Simply go to the Album tab, tap the menu in the top-right corner, and select "Bulk Download".
Downloaded photos and videos can be viewed by doing the following.
On iOS devices:
Open the Photos app.
On Android devices:
Check the Download folder on your device.
On most Android devices, you can check the Download folder by going to the Google Photos app, going to your library, and tapping Download.
Please note that names of screens and folders may differ slightly depending on your Android device.
(For iOS devices, the maximum number of items that can be downloaded at once is 100.)
Note: When one member subscribes an album to Premium Pro, all members of that album get access to Premium Pro features.