Bridesmaids duties

The only requirements is that they show up to the wedding in the appropriate attire. Anything above that is up to them. While not mandatory, they often will throw a bridal shower and bachelorette party. Any wedding planning is up to the couple getting married.

The only true duties they have are to wear the attire you specify and show up on the wedding day. They most commonly will help plan a bridal shower and/or bachelorette party, but those are not required. If they decide to plan those events, they will need to discuss among themselves to come up with a plan. You can always invite them to participate in other wedding planning events such as dress shopping or food tastings, but they are not required to attend those.

Purchasing a dress and showing up on time, in the attire you chose, to the wedding.

If you need help setting up your wedding they definitely can help you.

As others have mentioned, be there and support you on your big day with their dresses. But to be specific, a bridesmaid or MOH would hold your bouquet during the ceremony and bustle your dress for the reception (unless you have someone else doing those).

The members of the bridal party are in charge of purchasing the dresses you tell them to, and showing up on time to your wedding. Sometimes they choose to do other things like throw you a bachelorette party, but this is not a requirement. The MOH also usually holds your bouquet during the ceremony and helps you manage the train of your dress, if you have one.

PP have covered what the bridesmaids are/are not responsible for. If you post the tasks you are worried about completing, maybe we can help you brainstorm how to get everything done.

They’re supposed to show up on time the day of the wedding wearing agreed upon attire. The MOH usually signs the marriage license, holds the bouquet, and adjusts your train during the wedding. She will often give a speech at the reception. The bridal party should also be present for the rehearsal.
Beyond that, it’s all optional. If they ask if they can help with anything and offer to assist, you can take them up on it. For instance, I’m in a wedding and we helped address Save the Dates. I wasn’t MOH but was planning the shower and bachelorette (before it was postponed), but I offered to do so. The bride never asked for help or anything. I was the one who asked her to meet to discuss the events and offered more than once to help with various things.