When you go to a pre-party of a friend, you take your own alcoholic drinks with you.
If you invite your Swedish friends to your own pre-party, they will obviously do the same. This doesn’t mean that they don’t appreciate your hospitality if you offer your own, no, it’s just that alcohol is rather expensive in Sweden and they don’t expect you to pay a lot for a inviting them over.
Also, Swedes don’t like to feel that they owe something to someone. It is quite common that Swedes might accept your invitation for a drink, but soon they feel obliged to do a favor in return in one or the other way.
However, inviting Swedes for a pre-party and a drink is always much appreciated and is a good opportunity to connect with them.