How do i help these plants

Lower leaf yellowing would imply a lack of Nitrogen...but from the pictures, the veins in some appear green while the leaf is yellow - which is *usually* Magnesium issue. When the colour fade goes from the tip of an old leaf and works its way into the stem, you know you usually have a Mobile nutrient issue (Nitrogen, Potassium, Phosphorus, Magnesium) - the plant is canabilising itself for feed The picture of the leaf you holding looks like it has been chewed upon by something too! Ensure you don't have nutrient lockout by checking pH of water in and then the runoff water (You should be in and around pH6.5 for soil I believe). If you're in a soft water area, try adding CalMag to ensure thats not an issue. After that, if you can check roots to ensure they're not damaged/rotten, do what you can there in case of root rot or the likes (basically the plant cant take up anything and thats why it's slowly dying) and maybe try something to ensure no bugs around the plant (Neem or another food safe insecticidal).

You have problem with over nutrient, the soil have inside some nutrient, yours i think a lot ( watch the ec on the pack) you plant needs only water for a while