Bullfinch chicks didn’t survive

My husband and I have had the privilege of being so close to see a make and female bullfinch try unsuccessfully to raise their brood. The nest was in one of our potted trees at the back door, we were concerned with the location, however, everything seemed to be going so well for them. On Sunday there was 3 chicks in the nest. 

This morning my husband ran into the bedroom and said that the chicks were dead (gone from the best) and that there was blood around. We were devastated. It is just so sad for the parents, who have been working flat out for the last month, making the nest, laying the eggs and then mother bird sitting on the eggs for over 2 weeks to incubate them and now they are all dead. It is such a hard life for our little birds and we understand so much more now. We are thinking a dreaded cat got to them in the night. But then I was thinking of the Magpies and how they would have taken them from the nest. We have so many Magpies around that it is very concerning for other garden birds nests now. 

Will the bullfinch’s try again? Really hoping that they can raise a successful brood (fingers crossed) Heart Also how do you keep magpies away from our garden?