Some suggestions that I hope will help ( for reference, I am a real super-light packer, did 6 weeks in the far east with under the seat small rucksack only). Slightly different with four, esp. teenagers who apparently "need?" all sorts of crap, and @AuntieDen makes a great suggestion to go back into your booking and get ONE 10kg cabin bag between you ALL to take on, you can still do this, and it is not "one suits all" with the budget airlines - you can just add one carry on bag for one person. My other tips would be 1) wear the shoes/trainers that you will be wearing most of the time, and make them work with your outfits 2) you do not hardly any toiletries, the hotels, even airbnbs supply them, although I always go with DEET type stuff - jungle formula type stuff (roll on is best - a little goes a long way, the aerosols just make you choke, strongest is best) long sleeves and trousers at night are the best defence 3) Suncream, travel pouch, factor X to suit the most "burny". You can buy deodorant from everywhere in Prague, usually cheaper than you can in the UK, but if you must, then travel with one between you under 100ml. I also take travel toothpaste just in case, but it is the same story. Always toothbrushes. 4) You do not need outfits for day and night, unless you are going to high end restaurants, Prague is very relaxed. Although if you are visiting churches they may ask that your arms / legs above knee are covered. Work out what you think you need, then half it. It's OK to wear the same clothes when you shower, unless you are particularly insta-concious 5) check the weather, it will be hot, you almost definitely will not need your coat, but a cardigan or light fleece is helpful. 6) Because I travel for such a long duration, I wash my socks and underwear through (nobody can surely takes 6 weeks worth ?) but this is not for everyone. 7) I don't wear a lot of make up, but I decant a small amount of foundation and good face cream into a small travel tub, travel mascara, perfume sample. 8) Finally - do not try and overcram the small bags you have been allowed to the max, they "may" make you put it in the measurement device, and it absolutely has to fit, you are often not allowed to transfer things between bags at the gate, they can be lax, they can be strict, backpacks are usually given more latitude unless they are clearly overloaded.
Hope this helps, have a great trip. xx