Nelson, from past experience (I'll go into more detail in a bit) the only animal other than an anemone a pair of clowns can host successfully are softies.
I had a gorgeous 16"-18" swirling wall hammer for almost five years in my tank. My clowns hosted it for almost two years before they ultimately rubbed the polyps to the point of abbrasion and death.
After the wall hammer, they moved to my beautiful, but smaller, red lobo. It only took about 8 months until they killed this beauty.
With no home, they moved on to my 50-60 head torch. Once again, only about 8 months and they put another 'notch' on the proverbial headboard.
Now with three of my prized LPS gone I figured there'd be no reason to not get an anemone. I avoided anemones for almost seven years fearing they would wander the tank and sting coral or get mulched by a powerhead.
I picked up an RBTA. It didn't take the clowns but two or three days to find it, and have only left it to pick at food or move to one of the now two clones that have split off the original.
So unfortunately, my statement that softies would be the only likely host for a pair of clowns comes from experience.
Best of luck with yours.
R