An understudied and sensitive topic nowadays is that even subthreshold symptoms of autism spectrum disorder (ASD) and attention-deficit/Hyperactivity disorder (ADHD) in parents may relate to their parenting styles. The aim of this study was to explore the influence of (the combined) effect of child diagnosis (ASD or ASD + ADHD affected/unaffected children) and parental ASD and/or ADHD on parenting styles. Ninety-six families were recruited with one child with a clinical ASD (+ADHD) diagnosis, and one unaffected sibling. Parental ASD and ADHD symptoms were assessed using self-report. The Parenting Styles Dimensions Questionnaire (PSDQ) self- and spouse-report were used to measure the authoritative, authoritarian, and permissive parenting styles. Fathers and mothers scored significantly higher than the norm data of the PSDQ on the permissive style regarding affected children, and lower on the authoritative and authoritarian parenting style for affected and unaffected children. Self- and spouse-report correlated modestly too strongly. Higher levels of paternal (not maternal) ADHD symptoms were suboptimally related to the three parenting styles. Further, two parent-child pathology interaction effects were found, indicating that fathers with high ADHD symptoms and mothers with high ASD symptoms reported to use a more permissive parenting style only towards their unaffected child. The results highlight the negative effects of paternal ADHD symptoms on parenting styles within families with ASD (+ADHD) affected offspring and the higher permissiveness towards unaffected offspring specifically when paternal ADHD and/or maternal ASD symptoms are high. Parenting training in these families may be beneficial for the well-being of all family members.