14. His father asked him to stay at home because he was sick.
Because of ..his sickness his father asked him to go stay at home.....
15. Although his English was good, he wasn't chosen.
➡However  his English was good, he wasn't chosen.
16. Even though I admire his courage, I think he is foolish.
➡I admire his courage. However, I still think he’s foolish to do such a thing. 
17. However friendly he seems, he's not to be trusted.
➡ Friendly as 
18. Come and sit down, whoever you are.
It doesn't matter
19. You do any job, you should do it devotedly.
➡Whatever
20. Although she was ill, she went to school.
In spite of.