Croup?

Okay so i has this really runny nose for what felt like weeks, that got worse in the last week of having it where I couldn’t Breath, I thought nothing of it at first, as I thought it was hayfever, but I did have a cough for about a day, no crazy cough just a little cough for one day, well my two children including my 5 month old got whatever it was to, but now here we are two weeks later and my three year old has not got a runny nose anymore that went a week after mine, (but she did get it a week after me) and my son developed a cough about 5-6 days ago that got worse around 3-4 days ago and although my daughter does have a cough hers sounds just like a normal cough where my 5 month old sounds really raspy, and gets worse at night time and does worry me when he starts coughing, as it never goes, my question is, how’d you know it’s croup?can the doctors do anything for it? There not just going to tell me that I should go home and let him drink plenty if I go to see them? I don’t know what to do but it’s not getting better and every night is the same, it’s starting to worry me now. P.s sorry for the long winded questions, I’ve put a small video in comments where he’d fell asleep for a feed and started to cough.