Sick babies

My 3.5 y/o and 5 month have been sick for a week now with congestion mucus draining causing cough. My baby had a low grade fever one night but not since. I just don’t know when this will go away. We’ve been quarantined from cousins and they are dying to go out and be around other kids. I just don’t know when they will be not contagious. My oldest was congestion for a month in January. Thoughts or suggestions? My older refuses saline and suction. I’ve just been giving her vitamins.