Если использовать конструкцию be going to, то должно быть так:
1) They are going to play tennis
2) She is going to visit her grandma
3) We are going to walk in the mountains
4) We are going to wash the car
Если использовать конструкцию be going to, то должно быть так:
1) They are going to play tennis
2) She is going to visit her grandma
3) We are going to walk in the mountains
4) We are going to wash the car