Yea, "toughen up" can be translated like "坚强点！”"“振作起来！” ，but usually people who are closed the family would say something like this. If you are not familiar with the family I supposed, it's not proper to say that. If so, you could use "请振作起来。”

Culturally speaking ,it's impossible to toughen up, especially in the funeral, so it's not a good idea to just tell those who just losed their love toughen up.