Do you mist the leaves? Dry tips to the leaves of houseplants sometimes occur when the atmosphere is too dry for them - particularly likely at this time of year when the central heating's been one for much of the time.
Try misting them, and possibly standing the pots on a tray of pebbles and water - this will moisten the atmosphere around them. You won't cure the leaves that have the brown tips already, but hopefully you'll prevent any more appearing.
It could also be over-watering-they do not put on much growth in the winter and only really start getting going now-only water when needed even to the point they wilt-rather than on a regular basis
More house plants are lost through over-watering than anything else
Misting the leaves regularly really does help a lot of plants stay healthy, stops a lot of bugs too. I never had any luck with peace lillies, think I like the heating on way too much for them. If you have a badly affected spider plant, I have been known to trim off the brown tips. Wont save that leaf but does look a lot better