Urgent Help Needed to Save Stray Cat

Hi guys, I had around 12 stray cats living in my backyard. It’s a family of 3 generations; every single one has lived in my backyard because my family and I give them food, so they stuck around. Out of the 12 cats, 6 already died in the past week, 1 each day. They might be getting poisoned by someone in my neighborhood because they have been dying very quickly.

As of right now, the mom has been fighting for her life for the past 4 days. And one of her babies is also sick; it can barely see from its eyes because they’re so puffy. It's also having issues breathing. Her 2nd generation cats all died; there is 1 left, and he is showing symptoms of getting sick as well. His symptoms are just starting, so he might have a chance to live. I didn’t have a chance to save the others because it happened so fast. I at least have to save 1; anything helps. I’m willing to go half on whatever the bills cost to save their lives.