Even if the LLCs two member are mother and daughter or husband and wife, the entity is still a Multi-Member LLC, if the LLC has two+ members. Even if you qualify to claim her and your son as a dependent (which it sounds like you might), it does not effect the LLC.
The IRS did not create a tax form for the LLC. Multi-member LLCs default to be taxed as a partnership, while single member LLCs default to be taxed as self-employed. A single member LLC has less administrative burden when it comes to taxes.
The partnership form 1065 is due by March 15th and provides a schedule K-1 (1065) to each partner. They'll need to include the K-1 with their taxes. You can use TurboTax Business software to do this return, which can be found here: https://turbotax.intuit.com/small-business-taxes/
