If you want here's a link that you can use to create a link to download all photos from your Google photos account:
https://takeout.google.com/u/1/?hl=en&utm_source=google-account
(This is a site used to download data from your Google account including emails and stuff but we don't want all of that so we will exclude that in the next step)
Simply login to your account
Click on deselect all as it has extra things that you definitely don't want
Scroll down to Google photos and select the checkbox, you should also see an include all albums option or something, from where if you want you can even choose which albums you want to download from Google photos.
Scroll down and select next step, you will now have to select a delivery method i.e. if you want it as a link or want to upload it to a cloud service etc. After choosing this click on create export and wait for some time (ranging from a minute to a couple of hours) and your file/link will be delivered to you according to what you chose.
Download the files and cross check if you have all your photos and only then delete them from your device.
PS. For the photos that you have already deleted have you checked in the recently deleted folder at the very bottom in the gallery on the albums page?
Click to expand...
