Can I adopt my sister's 3 children, who was deprived of parental rights?

You can, but on the condition that the father of the children will also be deprived of parental rights or that he does not exist at all.

According to Article 213 of the Family Code of Ukraine a citizen of Ukraine has the priority right to adopt her:

• in whose family the child is raised;

• who is the husband of the mother, the wife of the father of the adopted child;

• who adopts several children who are brothers, sisters;

• who is a relative of the child.

Of course, you are a relative of the children, besides, you intend to adopt all brothers and sisters, but if the natural father of the children is not deprived of parental rights and is able to support the children on his own, then he will have an advantage over you. After all, he is his own father.

Also note that you meet the requirements of Articles 211 and 212 of the same Code.