Conflict over resources is a fundamental component of family life. Family conflicts are predicted to be strongly influenced by resource availability and levels of relatedness between family members. Here, we examined the effects of these factors on intra-brood sibling conflict in a family living beetle, Nicrophorus vespilloides, where offspring are partially dependent on parental provisioning. Specifically, we measured the intensity of offspring begging behavior in response to experimental manipulation of 1) relatedness between siblings (through mating females monogamously or polyandrously) and 2) resource availability (through varying the amount of resources at the onset of breeding). We found no effect of polyandry on sibling conflict or patterns of female reproductive investment, but we did find that sibling conflict was influenced by resource availability. Specifically, larvae spent more time begging on smaller carcasses, but only in smaller clutches. In addition, we found that resource availability affected patterns of female reproductive investment: when resource availability was low, females laid eggs more synchronously and produced fewer eggs but of a larger size. We discuss potential explanations for these results, and the implications of this study for understanding the factors that mediate family dynamics.