From the IRS point of view sub companies without an FEIN are the same as the mother company. Just add their names and profit and loss on your taxes.

Sub companies with a FEIN but not incorporated are the same as the mother company, nothing extra to do here either.

Sub companies with a Fein and Incorporated as a LLC is just multiple companies, just add them to your taxes the same you would if you worked at 2 jobs.

Sub companies with a FEIN and incorporated as a Corporation is no longer a child and must do its own taxes separately.

There's nothing to "Structure" really because IRS don't care where your money is coming from, as long as you report that it is coming from somewhere so it can be taxed and tracked.

I'm not an accountant just a fellow business owner, and i've been successfully doing my own taxes now for over 20 years.

Sounds like your attempting to use an LLC for liability protection.

Be way simpler + way cheaper, to just run the entire operation as a Sole Proprietorship + join a legal pool like Legal Shield (Ada Oklahoma) which provides support in all US states + territories + many overseas companies.

No entity will keep you from getting sued. People can sue you for anything, anytime.

If they're suit is wrong, it will be thrown out + you'll still have to pay attorneys fees.

If the suit is valid, no entity will protect you from fraud. This has been proved over + over again in court cases.

When court cases are involved, right or wrong does not apply.

The winner is the person/company who can go longest without going bankrupt.

If you're paying $100/month for unlimited coverage from a pool + the person who's suiting you has to pay $300+/hour for a competent attorney, you'll win...

Because you can outlast them.

Use a legal pool + when you get sued, work with your attorney to bankrupt the person suing you... by flooding them with court documents which they must answer + pay their hourly attorney fee... or drop their case.