Using newspaper under the grate is fine. It will make for easier clean up of the side out tray.
Those flexible plastic cutting boards illusive is talking about work great for covering the grate so they have a flat surface to walk on..and yes, also very easy to clean, and pretty cheap to buy also. smile
Just be sure to measure your cage before you pick up the cutting boards so you are sure to buy enough to cover the bottom. They may be a bit larger than the cage bottom, but they can be cut to fit.
IF you, or mom, have enough try to get TWO sets..that way when you take one set out to clean you'll have another to pop right in its place.
IF removing the bottom grate does not leave a big gap at the bottom where your birds could get through, you can remove the grate completely and just line the tray bottom with the cutting boards..or cheap white paper towels for easy quick clean up.
I use paper towels. The cheapest I can find at dollar store.

They really do need a larger cage if the one they are in is only 16 1/2x 11.8 and 15H. I think the smallest for 2 keets should be at least 18x30x18H..which is a flight cage. Bigger than that, double that, would be best. So start saving any way you can for a bigger cage. Look on ebay...and you can even start checking craigslist, sometimes you find used cages there really cheap. You have to keep looking tho because there may be none one day and then someone lists one the next.
If buying a used cage it must be thoroughly cleaned/disinfected before using it for your birds.
If you have access to SAFE branches you can use them to make natural perches to give them a little variety without having to buy them.
Here is a link to toxic and non toxic wood and foliage, fruits n veggies for birds. You need the NONtoxic of course.
Bookmark the page so you can find it easily to refer to in the future. wink
If collecting branches do NOT get them from a roadside where they have been exposed to toxins, and be sure they have not been sprayed with pesticides. Know the area you are getting branches from