Amity is correct, two hamsters who haven't grown up together since a very young age should NEVER be introduced to one another at all under any circumstances. Besides the fact that even sibling and pairs who have grown up together often fall out as well despite being together their whole lives. As mentioned above, it's simply not a natural setup for them and should be avoided if possible. Pairs that have grown up together (siblings) and have never been seperated can be kept with one another, but this is a stressful situation and takes a lot of time and heartbreak to ensure all is right with them, and in the end, you could find yourself coming home to a dead or severely injured ham
If you really want another hamster, why not instead you get another large enclosure and simply keep another in there?
Best wishes