Watering can be really difficult or it can be very easy. If you aren't sure when your plants need water pick them up right before you water them. If they feel light they need water, if they feel heavy they don't. Of course you're now wondering, "How am I supposed to tell if they are 'heavy' or 'light?'"
Easy, fill up a pot with the same soil you used for your other plants. After about a week the moisture in the soil will evaporate and now you have what a thirsty plant will feel like. After doing this a few times you'll get to know how light a plant is when it needs water.
And you should NOT water all your plants at a time if they don't need it. I know it may suck to have to water on different cycles but you'll end up killing you plants from too much or too little water.
It's natural that your larger plants will need more water than your smaller plants so you just have to deal with it if you want your plants to be healthy. Using clones will help you avoid that but cloning isn't really worthwhile for people only growing a few plants at a time; WAY too much hassle vs. simple seeds.