Yes and no on the ducks...I incubate duck with chicken at 45%, but lockdown chicken at 65%, duck at 70%, so until lockdown its fine.
Even saying that, I've also hatched duck and chicken together in the past (by setting duck a week earlier) at 70% lockdown.
In your case, because the ducks go on for a further week in a different incubator, you can increase the humidity a bit in that extra week to compensate for the 18 days they were at lower than is ideal. I've done it maybe 8 or 9 different hatches with good results. Just like the weighing method where you adjust humidity to keep weight loss on the right line, its the average humidty over time that matters, up until lockdown when its more critical to maintain it.