Constraints on α and β from two sibling pairs. The β constraints are from the pair analysed in Biswas et al. (2022) (high Δc, low Δx₁), and the α constraints are from the pair ZTF18abdmgab-ZTF20abqefja (high Δx₁, low Δc). The figure illustrates the orthogonality in the constraints from high Δc (low Δx₁) and high Δx₁ (low Δc) sibling pairs. We chose this as a specific case to illustrate that a single pair will have a degeneracy in the α-β plane. However, this degeneracy can be broken by combining the constraints on α-β with constraints from a siblings pair that has orthogonal degeneracy in the two parameter plane. The combined constraints in black are for illustrative purposes; the final constraints on α and β from the combined sample are more stringent than presented here.