grad gift blended family

My husbands friend of many years(they only really socialize for hunting, the friend came to our daughters wedding 8 years ago and a grad party. The friend, Jim, has always lived about 3 hours away. When he remarried 3 years ago we went to the wedding, his new wife came with 3 daughters and he had a daughter and son we know somewhat. We have only met Betsi, the new wife, beifly 3 times and her daughters VERY beiefly at their wedding (in the reception line). His son and one of her daughters are both graduating from high school next week. We recieved an announcement/open house invite for Josh, his son, and in the same envelope one for her daughter, who we don't know. We expected the one for Josh but not one for Katie. The question is...... how do we respond in the gift department, we cannot attend the open house and would normally send a gift of money to Josh. Are we expected to send a gift to Katie? Is it expected to be of equal amount or should we split the difference so to speak and send a little less to him and a little more to her (ending up equal) Or do we even need to gift the stepsister since we don't know her at all or her mother very well??? If this is confusing I apoligize in advance.
Thank You, Not Sure What To Do

Dear Not Sure,
You are not required to give a gift to the graduate unless you attend the party, but I understand your situation. Send a card and a token gift to the daughter--there are people who will be in the reverse situation--and send the boy whatever you were originally going to send him.