Leylandii dilemma

Hello I'm new to this but could really do with some advice,

I've recently moved into my new house and it has around 10 leylandiis in the garden that tower over the house! At first I was adamant these would get cut down and then start landscaping my garden (I even got several quotes)

But then spring arrived and it wain't to long befor house sparrows started appearing out of the trees, so I brought a feeder and over night the garden became a bird a hot spot. My garden now attracts attention of

2 collared doves nesting in the neighbouring tree 

blue tits who visit weekly 

a Robin who visits daily 

A long tailed tit 

and several house sparrows who's took nest in the leylandiis 

including a squirrel  

the issue is I don't want to loose my bird paradise but these over grown trees need to loose height and become less over grown but doing so will I scare them all away or loose my gardens bird appeal. has anyone had any situation like this and what was the out come?

here are some pictures of the local bird population I've managed to spot