Yes it will work with only max-limit on the parent queue, and just priority for the child queue. Priority does work with no max-limit on on the child queues.
Things are not perfect though, it can take a bit to ‘catch up’. With SIP this can cause a little jitter (audio fluctuation) when starting a large download. So I set the max-limit on the child queues to leave a little headroom for VoIP.
Limit-at is ‘guaranteed’ bandwidth. The sum of all child limit-at must be lower than parent max-limit.