I would like to know if I should still go to the doctor despite the absence of fever and other symptoms or can I wait?

My 3 and 1 year olds have been coughing for 2 weeks. My 5 year old daughter brought home a cold from school in September and since then the bug won't leave the house. The whole family was tested for covid last week to take no chances as the kids kept coughing and having runny noses. We all tested negative. My 5 year old daughter has not been sick since but now my two youngest ones can't stop coughing and it's very greasy and they have a lot of secretion. My boy is vomiting so much that he is full. We do the baby fly repeatedly every day and I give them the helixia syrup but no improvement. They do not have fever and have never had a fever since the bug arrived. Their condition is super good, sleep is as usual. It's only the cough that worries me after two weeks I tell myself that it will eventually pass but nothing.