Took Guppies From A Desperate Moving Friend And Think They May Be Dese

I took guppies from a friends who couldn't find someone else to take them, i feed them two pinches of fish food twice a day, turn off the tank light at night, i have small ornaments and a couple plants with little leaves. I measured levels today and all were stable (maybe ph slightly edging over usual range). I forgot to clean the tank filter last water change but i took them out and cleaned it today as well just in case.
In the past two days I have arrived home in the afternoon to find a guppy each day turned totally white, sunken to the bottom of the tank and dead. I have no clue what could have happened but I really want them to be healthy for when I get someone else to feed them for a few days so nothing unexpected happens without me there.
I asked the previous owner about the condition and she said that she hadn't seen it happen with her fish before.
I can't tell if they are acting unusually because I have only had them for a short time but I could say that they tend to go to the top in groups sometimes or the bottom (what I think is) picking up scraps dropped by other fish.
Other details might include I had/have a few pregnant guppies (I think possibly a birth but I wasn't present), I don't separate guppies in labor because my friend previously tried and says it over stresses them and they don't tend to eat their young, I have had the tank almost two weeks, I can't tell if their pale bellies are natural, there are no other white spots on them and they don't appear slimy or fuzzy and the tank has no exposure to sunlight and cleaning products.
I don't know how much of that was necessary (sorry) but this is really stressing me because I don't want to fail my friend.
Some may have inflated stomachs slightly but I can't tell. I didn't check the gender of the fish and the one that died yesterday lacked half a body and back fin, showing a spine and bones.
(blurry photo of a dead fish at the bottom of the tank)

You have only had your tank set up for two weeks? If that's the case, your tank isn't cycled. Can you let us know the amount of ammonia, nitrite and and nitrate present right now?

Agree with AmtotheBurr. It's not clear what you mean by cleaning the filter, too. If you're giving it a total clean with tap water then you'll kill the ammonia-eating bacteria that's needed in a cycled tank. If the tank is uncycled, then do daily water changes with conditioned water until the tank is cycled. Leave the filter alone, except for squeezing / rinsing the sponges in the old water before you pour it away.