Замените формы глаголов Present Continuous формами глаголов Present Simple.1. My relatives often spend much time together.

Вероятно вы имели ввиду заменить Present Simple на Present Continuous так, как глаголы уже написаны в форме Present Simple

1. My relatives are  spending  time together.2. He is teaching mathematics at school.3. They are visiting a museum today.4. Helen is meeting her friend near the university today.5. I am introducing my new friends to the parents today.6. People are setting up a customhouse for the examination  of foreign goods.7. The fortress was re­placing the custom-house in 1761.8. The inhabitats is nicknaming the don river as Father Don.9. People are calling Rostov on Don the Gateway to the Caucaus.10. They are restoring that church.