Single Member LLC; Can You Add a Member?

[Sheldon Kirk]

Ran into a tricky problem this weekend & am wondering if its one anyone else has experience with. Any help is appreciated. So several years back I started a self-directed IRA to buy Property Tax Certificates. The IRA invested into a single-member LLC i control, "LLC #1". Then two years ago I started a self-directed HSA to also buy tax certificates and had it invest into a single-member LLC i control, "LLC #2".

After a while of having two LLCs and the costs that go with them I asked around & was told that my IRA and HSA could both invest into the same LLC. Nice!

However now I am trying to figure out how my single-member LLC #1 can add a new member (my HSA) and be IRS compliant. When i created it, it defaulted as a disregarded sole proprietorship. It looks like I would have to elect with the IRS to change this LLC from a sole proprietorship to a partnership or corporation? If so, will I also need to start filing tax returns for the LLC with the IRS?