Hello and thank you for asking the most proper behavior with regard to etiquette, which does, as a matter of fact, have a rule book for these issues. Unfortunately, those rules are not going to give you the answer you might want to hear.
According to the strictest rules of etiquette, gifts of any and all kinds are to be given without any expectation of a 'thank you' in any way. That is the hardest thing for most gift givers to do. It's like loaning people money. The rule of etiquette with that regard is to never ask for or even expect it back, unless of course one is making an official, 'on paper' loan.
As gift givers or money loaners we have the choice of not giving gifts or money if the other party does not follow the rules of etiquette set for them.
Yes, the recipients also have an obligation and this is the part you'll like hearing: As a recipient of a gift they are obligated, according to proper etiquette, to extend a formal 'thank you' within a reasonable amount of time (typically within a month) after receiving that gift. I adhere to and teach 'old fashioned' etiquette and insist on issuing a tangible, snail mail thank you card. I raised my own children this way and I teach everyone in my classes ranging from Kindergarten children to high level executives to do the same. Not an email, not a phone call - at least not by themselves. A genuine thank you should be issued no matter what.
That said, these days I groan and accept that email or phone calls seem acceptable for most people; however, from your posting, you're not even getting this.
So the bot***** *****ne with regard to the rules of etiquette is that you cannot bring it up with sarcasm and you cannot ask for a thank you. What you CAN do is stop giving gifts. This is not only perfectly acceptable, but it appears to be in order.
If anyone is so low brow as to ever ask you why you stopped THEN you can calmly say, "I find no point in giving gifts that are not appreciated" and bite your tongue after that, say nothing else and rise above it.
At that point you might find yourself deluged with 'thank you's' and you can decide whether or not to resume the gift giving, but keep one thing in mind most of all: Gift giving is supposed to be from the heart of the giver and done without expectation of acknowledgement in any way. It is supposed to be because the gift giver feels good about enhancing or enriching someone else's life.
If you are not feeling good about giving to these people, then stop. Send a card and a nice note - investing no more than a couple dollars and a few minutes of your time to note whatever occasion it might be.
My colleague has offered more real world 'relationship' advice that has it's own merit. I'm just addressing the rules of etiquette with regard to gifting and thank you's.