One day Karolina got to know that she 'will' (lepiej uzyj slowa 'would') have a brother.
After nine (mozna dodac 'long') months Karol was born. When he was six months OLD 'in the house fire broke out' (zla kol slow - a fire broke out in the house). The fire 'diffused' (czy masz na mysli 'spread') very quickly.
THE smoke was dense and stifling. The firemen saved Karolina and her
parents, but iN the middle of THe (tu mozna dodac 'smoke-filled') building Karol and Atos 'stayed' (lepiej 'still remained').