As I mentioned these are the healthiest and the easiest to maintain (see pick) and one per room should do it.
You mentioned dogs, so you would have to place them higher up as do I.
I use attractive vintage bowls that are 3"-4" high with the smallest being 12" in diameter and they last 2-3 days during the winter and/or during the Santa Ana winds.
If you don't want to use bowls then 2nd best (health wise) would be an electrical "cool" evaporative humidifier (avoid the warm mist designs).
They require that the filters be cleaned or replaced often.
Ultrasonic humidifiers needs to be kept impeccably clean/sterile as otherwise they can spread bacteria in a very fine/breathable mist which is a health hazard to everyone in the household.
They also require extremely pure water (like double distilled) in order that they operate/mist as designed.
I've had allergy/sinus problems since the 80's which is why I'm so picky and why I no longer use ultrasonic or warm mist humidifiers.
DeKay