Specifically, a domestic LLC with at least two members is classified as a partnership for federal income tax purposes unless it files Form 8832 and affirmatively elects to be treated as a corporation. For income tax purposes, an LLC with only one member is treated as an entity disregarded as separate from its owner.
you have a multimember LLC,which files a partnership return and would be required to continue filing a partnership return through the date the number of members is reduced to 1. That can be done in two ways. first, one member gifts the other member their entire interest in the LLC. This may require filing a gift tax return. Second the LLC redeems the entire interest of one of the members. Since I don't know what's involved in the LLC talk toy your accountant.
once it's a single-member LLC it can no longer use the partnership's, EIN.
the single member entity, for security purpose, if it must issue 1099s or W-2s should get its own EIN for the owner. Otherwise, their SSN can be used. However, if 1099s or W-2s need to be issued, do you want strangers getting your SSN? Generally, a multimember LLC can not covert to a Qualified Joint Venture.
Consulting with your accountant would be appropriate
