We need to become better people if our priority is our children.
We have to become better people if our children come first.
We really have to work on bettering ourselves if our children are our priority.
最優先（にする）：priority, come first, put ... first
人間的にもっと成長する：become better people, grow up, better oneself
* We have to grow up ourselves if we want to put our children first.
（子どもを優先したいなら、私たち自身が成長しないと）
必要がある：need to, ought to, should, be necessary to, have to
おまけの英訳：
We really have to work on ourselves if our children are the priority.
We should grow as a person so that we can give the first priority to children.
We need to grow personally so that we can think of children as the first priority.
grow as a person = 人として成長する
grow personally = 人間的に成長する
give the first priority to ~ = ～を最優先する
think of ~ as the first priority = ～を最優先と考える
そして、should も need to も「必要性」を伝える表現です。
アメリカ合衆国 
日本 
