Mid September or mid October wedding

Hi everyone. I need some advice. This may be confusing so bear with me. My future sister in law got engaged a month after I did. Due to some miscommunication, they decided on October of 2021 for their wedding. I have always wanted a fall wedding so I decided to hold our wedding in September. We recently booked for September 12th. Since then, my SIL has changed her date to early August due to venue availability. So here's the dilemma.



Our venue has an October date available but it is October 17th. We are planning a Sunday wedding anyway because it is $35 cheaper per person. Having it mid October would allow over 2 months of separation between the weddings. My issue is the weather. The venue has a retractable roof in the ceremony room and I would love to have it open. The weather in NJ is so unpredictable. It could be too hot in mid September but too cold in mid October. Otherwise everything else but the pictures would be inside. There are no pretty trees to worry about unfortunately as there are none in that area.
What would you do?