I have 6 1.25" kribensis in my 40g breeder. It has plenty of rock caves and a mat of fake hair grass that measures about 8x8" that they can hide in. There is no aggression whatsoever even with my 3 boule's and pleco.
Yeah you shouldn't have any problems if you add some caves. Separate them with rocks in the middle if you can and they'll love you for it! I'll post some pics of my tank here in 2 seconds for ya.
Round rocks like small cobblestones are ideal given their round shape. I use pumice due to its weight and cobbles as well. Boil them for 10-15 minutes and rinse em for a good 20 seconds and you'll be right as rain.