I lost my iPhone 6, How can I get the pictures back?

There's some very important family pictures that I'd like to have forever, and show my children and grandchildren maybe.

Unless you have them stored somewhere else, you won't be able to get them back unless you find your missing phone.

Dropbox?

Unless you backed them up to iCloud or another computer, they are gone. If you backed them up, you can restore from backup or usually browse them where they were backed up.