IZA - for your girls check out your local fine clothing stores to see if they have any holiday season dressy clothes on sale. Wedding boutiques are a good place to find dressy clothes. Any store that carries any kind of "party" clothes would be fine for your daughter. You might have to shop on-line,there are lots of sites for formal/dressy clothes. Some of our major department stores have web sites - Nordstroms comes to mind. Your boys are easy, dress pants, dress shirt, dress shoes and a tie is all they will need.
Another place to look is if you have consignment or thrift stores- you can get great deals on slightly used clothing - especially sports jackets for the boys.
This may sound a little "cheap" but does Sweeden have a Walmart?? it's easter time and they right now have alot of girls dressy clothes. Also in the boys dept. you can find nice dress pants, shirts, and ties.