I think it looks like powdery mildew. I would remove any infected leaves and stems that look like they’re starting to show signs of infestation and then apply a fungicide (I like neem oil). I would get on this ASAP - it’s pretty easy to knock out if you catch it early but it can get gnarly fast if you don’t. I would also use the fungicide on any plants kept near this one to be safe and I would quarantine your string of bananas until it’s on the up and up!!

Looks like mealy bugs to me.

On second glance, I definitely agree with mealybugs or some other scale (I didn’t look at the last few pictures at first). If it were me and if the infestation is as widespread as I think it is, I would probably part ways with the infected plants rather than risk further infestation. Good luck!

Looks like mealy bugs to me too. To find out, get a q-tip; moisten with rubbing alcohol and apply to 'white fuzzy blob'. If mealy, the white fuzz will dissapear, and you should see tiny bug of darker color. Rubbing alcohol will kill it. If there are too many, maybe you should get rid of infected plant, as Morgan suggested. Small infestation could be eradicated by spraying with rubbing alcohol, but you said it looks like it spread to couple of plants - it would be difficult to get rid of them. Problem is that they hide very well, in spots that are difficult to see and treat. Mealy bugs spread easily to other nearby plants. There are some chemicals/systemic sprays that could be used, but I am not sure which ones as I never used any.