Together, we have over $200K (mostly in stock market investments), and our parents may help with the down payment.

If the other two parties want to flip a house maybe they can do just that as partners and then sell you the house which you can buy with a primary home loan with low down payment.

One has no mortgage, their other has a HELOC for around $20k remaining and is coming to its 10year term that was established before placing with LLC.My predicament is how/best way to pull equity out of either property for a down payment for the 3 family that is valued around $450k.

I'm looking to invest between $50k and $75k as the down payment. 

DSCR loans are based off of down payment, credit score and either actual or market rents so it helps to supercharge an investor's real estate goals and net worth.

You can even plan vacations that are written off if using the sandwich method by doing work on Friday and Monday for real estate and the weekend is there so you do vacation stuff so all lodging and travel can be written off. 

I assume you currently have a residential mortgage that does not have a pre-payment penalty.

Repayment options can be more flexible like in my case I do everything on accrual this really helps flippers when they dont have to make monthly payments.

Know that every long term lender will require a survey and if something comes up on it when you are trying to sell or refi, you could get stuck in hard money without an easy or quick way to get out.Is there a pre-payment penalty?

The front end can sometimes be tedious to get approved by the local housing authority, but rent payments are always timely.