I will give you a ready made co parenting and custody app with source code

Co-parenting apps cost families $150 to $600 a year, because almost every one charges each parent separately. In 2026 both free options vanished: AppClose ended its free tier in January, TalkingParents removed its free plan in March.

DuoNest is a working Android app (Kotlin, Jetpack Compose, Firebase) for separated parents sharing custody. An append only message thread, a shared custody calendar where changes are proposed and accepted, and expenses with a running balance.

Location, done properly: either parent can attach their GPS position to a message or a handoff, and either can ask the other where they are. The other side chooses whether to answer, and the ask and the answer, share or decline, both land in the record. No background tracking.

Every record is hash chained, so any later edit to history is detectable, and records are emailed out as they are created, so the history survives even if both parents delete the app. One tap PDF export.

A built in demo mode lets you explore the whole app before buying, with no account. You get the full source, Firebase rules and Cloud Functions, and the branding.