well the sanseviera prefers diffuse light and watering only when the compost is dry as it is a succulent. wrinkled leaves suggest not enough water.
the fern also likes diffuse light but prefers a humid atmosphere. so the brown leaves are due to the air being to dry. Mist the plant regularly.

I agree, when the leaves start to crinkle or look droopy, it's time to water, average about every two weeks.

Thank you for your answers. I do mist regularly, SBG, but perhaps not regularly enough. The Maidenhair was doing very well until I went away for two weeks a year ago. With nobody to water it I put that and the Sanseveria in the shower tray on a thick towel that I drenched. Alas, when I came back the fern (and the towel) was dry and very sorry for itself. I’ve managed to keep it going but it’s not exactly flourishing. I also think, Bathgate, that every two weeks is about how often I do water. Originally I had the plants in my north facing bedroom, with diffuse light from a slatted blind, but when Monty Don said they preferred the bathroom I transferred them. I’m now putting them back in the bedroom where it’s not so warm but if the fern doesn’t pick up I think I shall have to reluctantly give up on it. Thank you again.

if it is the British native Maidenhair fern Adiantum capillus-veneris then it is an outdoor plant but if it was bought as a house plant Adiantum raddianum, it isn't hardy and cant go in the garden. that may affect how it grows in/out doors.