If you can get readings from your dad's liquid test kit, there are literally hundreds of us here that can tell you what the readings mean.
As for your dad not letting you use it, I suggest asking him, and explaining why before just deciding that he won't. I can't imagine many parents being upset by the idea of their children trying to properly care for their fish, especially when they seem to be in the hobby themselves.
You can save yourself some money by not buying the carbon filters anymore. You can take a used carbon filter, cut it open, remove the carbon, wash it out well, and re-use it in the tank as mechanical filtration. Carbon doesn't do much for an aquarium aside from remove nasty smells (if they exist) and remove medications.
I don't think people are as upset that you don't have money, as they are that you chose to spend your money on test strips, which you were told by several people are not reliable. Cheaper or not, if the results aren't accurate, they're nothing but a waste of money. And as was pointed out before, although the price tag may be cheaper for test strips, when you factor in the number of tests you can do, the liquid kits are far LESS expensive in the long run. And if you intend to keep your fish for longer than a few months, the long run should be what you're concerned with.
You mentioned having "old" fish and assuming that that's why they're dying off. You also mentioned only being in the hobby for a year. Do some research online. You'll find that the average lifespan of most fish is FAR longer than a year, often up to 10-20 years (depending on the species). Just because a year may be relatively long to you, doesn't mean that it's natural if a fish dies after that long.
Most importantly, when you ask for advice from people more knowledgeable and experienced than you, believe me (as someone who made their share of mistakes when they were new to the hobby), you should give more consideration to what they have to say. They may not always be "right" (simply because there's often not just one right answer), but their advice is based off of far more experience than you have, and is given with the best interest of your fish in mind. It's at least worthy of putting some thought into, perhaps researching their suggestions if you have any doubts about what they have to say. If money is an issue, post about it here, and you can get suggestions for low cost options, or as in this case, assurance that you're better off saving your money until you can afford reliable equipment.
. The one I use is the extremely cheap plastic frame mesh one, that comes with these little metal arm things that you hook over the edge of the tank. It won't fit in the tank I needed it for with those arms unless I leave the lid off. So I took cheesy little suction cups made to hold air tubing (maybe 2$ for 6) and put them on. The easiest way I found was to pull the little pokey thing out of the suction cup, then shove it back in with the mesh wall in between. I have since switched to two heavier duty suction cups for ease of use, but the tiny ones worked fine. Then I had the little plastic tube holders along the top edge of the breeder.. I pulled a couple of the old plastic plants apart into stems, and clipped on. I figure that made it a little more private for mom, and provided some hiding spots for fry until I got her out. 