Another Kentia.

Looks like sun damage or overwatering. Is there sitting water on the dish?

There in half shade so I dont think its sun damage, no im careful about standing water, I try and give them a light watering when they need it but no more.

Is it indoors or out?. It looks like its had a change in lighting..to sun when it was used to shade.
Another is too dry. Air or roots. Look under the fronds for mites...they can kill a plant in a warm dry air room. In that case you would need to use a fan to circulate the air. Or..pesticides as last resort. But if conditions don't change..pests just come back.

Looks like sunburn to me.

They haven't been exposed to any sun, they live in a room about 12 feet from a net curtained medium sized south facing window and we are still in winter.

I think my larger Howea is dying, the fronds are turning pale and changing to brown. The very tips have turned brown on most fronds but I dont think it's dry air as I have a damp problem and a humidifier if the humidity drops. Its in a room with a medium sized Dypsis Lutescens which is doing well and they are alot more sensitive so conditions cant be to bad, can they?

Only thing I can think of even tho its in 5-1-1 mix for its drainage maybe ive put them in to large a pot and the lower levels of the potting mix is staying to wet, tho it is only a guess by an amateur.

More advise needed please