@RebelFighter ~ Wow. Tough row for you to hoe.
I am on Ancestry and am good at blocked walls.
Read all available documents throughally. I have found so many clues to further my search by reading old documents.
And you found your (RIP) father and 1/2 brother and first cousin. Fabulous!
Do you have American black DNA by any chance? Three generations probably takes you back to 1880's ~ 1900. Not far. Those DNA cousins of mine who's great great's were slaves have a very hard time with blocked walls galore. I have only been able to help one DNA cousin because his 1st and 2nd and last name was past down and also it was known where they lived. He was a 3rd great uncle's (slave owner) illigetimate son. (Same name as the slave owner).
And if you are American (I don't know) the early Colonists were very British with precise record keeping. Religiously, if they were Quakers, so much info is available.
In my Tree I have helped DNA cousins who have been adopted, and like you have had walls. Because my mother was like yours, a pathalogical liar, I am like a bloodhound on a scent to find the truth. I find it a fun challenge to dig the truth out from publicly available documents and expose their lies.
Many people have discerned that who their grandparents were, was something that they wanted to distant themselves from and start over. Change their name (your mother did) birth location etc. and especially age (so many kept making themselves younger in US Census through the decades). Lies, lies and more lies but it gave them what they wanted. A new start. Some had shady pasts and didn't want that name to be used (might get arrested?).
One of my ethnic groups is rare. On MyHeritage I have only 10 matches for this group. None of them know our vast history that my grandfather told me so I share and they are thrilled.
My suggestion is everyone should do it. I can't imagine what it must feel like to be adopted and not know...
