How Can I Make It Easier For My Kittens To Go To The Bathroom?

Maybe a cardboard box top lined with a garbage bag. Then put cat litter in the box. The edges are a little lower on some box tops but if this is still a challenge you can always place a garbage bag underneath the box and tear one of the ends open so they can walk right in to the litter. You won't need to use a lot of litter because kittens are tiny and they may have a hard time moving in the litter so just keep this in mind and watch them to see if there's anything else that you see that they would need help with. Or just simply to observe their behaviour to get to know your cats. This can be helpful as they get older because you can tell what's normal for them so if they do something different you know they may not be feeling well.
*I hope this helps you. Have fun with your kittens.

Use a cardboard box top because some of these tend to have a rim that is lower than a regular cat box. It will make it easier for them to get in and out of. Line it with whatever you want. I've found that the self clumping litter works really well and contains the odours. There are litters that are for multiple cats as well. Enjoy your kittens.