Looking at the pictures, the soil looks to be compacted, probably due to heavy watering. Try loosening the soil with a fork. Best to water with a fine rose watering can. if using water hose, set a very fine spray but longer duration. Try to let top part dry out between waterings.
For onion, garlics, break some egg shells finely and scatter on the top to repel snails. Ground coffee also can. The snails can be small and undetectable at first.

How much sunlight are they exposed to? Evening or morning sun?

I'm no expert but just some points for consideration...

http://ongzi-secretgarden.blogspot.com/201...garuda.html?m=1

https://mrkumai.blogspot.com/2012/11/info-t...garuda.html?m=1

If I'm not mistaken, this is Sansevieria..(common name mother-in-law tongue)
This is a favourite low maintenance indoor plant .. It needs the soil to be dry between waterings.. So once a week should be enough...
Sometimes, when we buy from nursery, the soil provided in the pot have very high water retention ... This is because they cultivate and keep the plants under plastic shade with controlled watering... When conditions too wet, the roots will rot....Best to change the soil by adding Tanah bakar (coarse red type)

https://www.joyusgarden.com/sansevierias-ak...ake-plant-care/

Hope this helps

If it's Cyperus esculentus, then I think you're out of luck. I think only glyphosate will work but then it'll kill your grass as well... Not sure if triclopyr will work and it's expensive.
Refer here
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7432.html

Best would be to dig up to 10 inches deep and get all the tuber chains.... They're like thick black threads with nodes and burn them... This will also get some aeration into the soil.. do a small patch at a time and replant the turf... Not difficult to get your grass back...
In future, you have to catch this weed before they establish by digging them up manually, slowly pulling as much of the chains without breaking them... When you see a shoot emerge they would have already developed extensive rhizomes underground....

Your problem is because they cut a hill right down to the subsoil to build your house (common here in Malaysia).. The earlier suggestions to plant in containers or raised beds are sound, just that they present their own problems with regard to water and nutrient requirements. Need to understand your unsuccessful attempts earlier..... Is there sufficient sunlight and water? What soil did you use?
If you want to grow anything in the ground you described, you need to add more organic matter...
Here's maybe something you can try.....
Dig a1ft wide X 1ft deep trench and keep the soil on one side... Wait for the Majlis workers to sweep all the leaves from the roadside trees which they collect in plastic bags... Ask them for this and fill the trench, then cover with the soil.. it should look like a raised bed (batas) now ...Make sure it's mounded up about 3-4 inches since the dried leaves will decay. This will also ensure the bed doesn't flood when it rains. You can try to plant the following plants...daun keledek, dill, ulam raja or Brazilian spinach (I'm assuming you have full/almost full sun)
Get a 10-12 gallon black trash can (old one also can) and drill some large holes (at least 1/2 inch) in the bottom and bury it about 6 inches in a part of the trench... Throw your kitchen scraps and any garden waste here... As they rot they will provide some organic matter to the surrounding... After some time, you can also use this rotted material to fill more trenches...
You can also try planting papaya(just throw the seeds from one you've eaten) or banana .. These 2 also quite hardy...
Also invest in a decent watering system... If you can diy, can get those from shopee/Lazada using 16mm ldpe piping... Quite easy... Otherwise get a watering can with a fine rose or use hose with fine mist so the soil doesn't get compacted further ..
Info on the suggested plants:
Daun keledek and Brazilian spinach grow from cuttings ... Put the 4-5 inch cuttings in a small cup of water until it roots (4-5 days)... Then plant in the soil...
Dill also grow from cuttings but plant straight on the ground... Don't put in cup....
Ulam raja grow from seed... Just scatter the seeds and cover lightly with soil...
Water at least twice a day...
Happy gardening...