To keep it as simple as possible: poly is about feelings, not just about sex. Most would classify a triad as a relationship configuration where all three people are romantically involved with each other. Could even be non-sexual involvement; just emotions. In a vee two of the three people aren't emotionally involved with each other.
Therefore the realtionship you describe is a vee. They don't have sex with each other, they are involved with you but are close friends. As long as they don't say that they are 'in love' the most accurate term would be a vee
Ah right; Edit: There is search function with tags. You will find 'vee' or 'triad' there.
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.