Not in the best condition

Hello, I'm quite worried about some of my houseplants and wondering what I might be doing wrong.

I would appreciate any advice as to how much and how often to water, why some have mould on top of the soil, and why the flamingo flower plant has some discoloured and crispy leaves.

Thank you.

 

They all look pretty good to me.
Maybe less water for the ones with mould on the surface of the compost, let the surface dry out between waterings.

As long as any brown leaves are the lower ones I wouldn't be that bothered, just part of the normal process.