My human daughters ear has a build up of wax like that, but it's not that brown. It's from allergies. I've Debroxed her ears & syringed them out. Not saying to do your chis, but I bet it's allergies & pollen if both of them are getting the buildup. You might ask your vet about an antihistamine for them. Buildup of wax can definitely lead to ear infections & that sounds like why Chicos ears are so red. Hope they get some relief soon.