As already mentioned, add some pee pads to areas where your piggies prefer to go to the toilet.
I've attached a photo of my setup (taken me a while to test/try different things). The yellow square is where I have a pee pad, hard to see as its the same fleece as the liner underneath.
I use a fleece liner on the bottom of the cage, with puppy pads underneath (absorb any wee that seeps through the liner). On top of the liner, I have another small liner in their house to make it comfy and incase they occasionally wee in there and another liner that i put next to the red tray in the photo, as this is where my piggies have decided to use as a toilet. The red tray is a cat litter tray i fill with wood shavings to put their hay inside and they also use this as a toilet.
(I use zorb inside my liners, its quite expensive to source in the U.K. but i found it worked well with me, however i haven't tried using anything else).
I've found that through this method, the longest i've gone without changing the liner is 9 days. I change the smaller pee pad liner every 2 days as this gets soaked quite quickly. I change the wood shavings in the tray twice a week and usually freshen it daily when giving fresh food/hay/water.