Help! My newborn seems kinda sick...?

I have 2 year old twins, one suddenly came down with a fever, vomiting and achiness on tuesday. We took him in yesterday and they said it looks like he has strep (from the way his throat looked) and he has and ear infection in each ear, so he put him on antibiotics. Today the other twin came down with the same symptoms except with a little bit of a higher fever. We also have a 4 week old who is now congested and coughing and at some points wheezing. I am just curious, what can u do for infants this little or do they need to be seen because of the age? I know it might sound dumb, but with two other sick kids a trip to the er seems like alot if its not necessary. Thank you.