Edge Constrained Vertex Coloring (ECVC) problems are defined on a finite multigraph, their solutions are characterized, and a linear time algorithm is given for solving $N$ ECVCs on the same underlying multigraph. Using ECVC problems we develop a novel family-based haplotype reconstruction method which has linear-time complexity in both number of markers and family size and has many other desirable properties. To do so, we define a multigraph given a genomic interval on which a family is recombination-free.