the type of gift doesn’t matter (except in terms of superstition, which can matter a lot

) so you do not have to give them the same thing everyday, as long as you give them the right value of stuff - three pumpkins and three coconuts should work exactly the same so give whatever is easier.
For villagers who are brand new it takes pretty much a month minimum, if you are gifting everyday, so I don’t think it sounds like you need to worry yet. Since your villager have some amount of established relationship with you already it may take less time, but I think it would be safe to assume you will be gifting daily for about a month.
if any of your villagers ask to set a secret greeting, that means they are at the correct friendship level to gift you a photo. They do not always set the greeting before you get the photo, but it is a good way to know what level they are at when you are feeling impatient.
this guide has some information on friendship mechanics, but please note that is has not been updated since august, and the gifting mechanics have changed since then (as described in this thread). But it is still useful in terms of understanding the friendship levels and how they work.
yuexr.github.io
(Sorry if this was already linked previously)
Again, it sounds like you are not doing anything wrong. It just takes time and patience (which can be frustrating, I know)