Would this be ok

Yes of course. Not that many are ultra orthodox anyway. One of my SILs celebrates everything, Christian and Jewish. I never serve him pork which is probably my issue, not his.

Why wouldnt it be ok?

I would ask the family whether they mind. It would be embarrassing if they saw them unexpectedly and didn't like it. I'm sure they'll be fine but it's just good manners to ask in their house.

might be best to check with the woman of the house.
presumably your daughter is a nanny; some households might object re influence on children, if they might see the room.
but then again the most observant would probably prefer a jewish nanny, i suppose.
best to err on the side of caution, i think.

I would ask first. However I would hope that it wouldn’t be a problem in these days of acceptance of all different views and ways of life.

Just ask , surely you would anyway, they may not want sellotape or tacks in the wall

Out if courtesy, i would ask, can’t see them saying no.

Yes, I think your all right. She should just ask. She was just thinking of an ornament or a little tree

There shouldn’t be a problem. We have syrian friends who always celebrate Christmas.

Always ask first. A woman at work decided to put up decorations by her desk. They had to come straight back down as they would have set off the security alarms if there were the slightest breeze and they moved.