i see two options here 1) you can go back to dad and break it down as hey i cant close on the house until it's vacant and see if he can help in getting them out, 2) offer some moving expense if the lot is really that desirable to you I know not what you want to hear as the investor but it has worked on numerous occasions, 3) you will have to take it to the courts as final resolution so the sheriff can remove them.

Most cities have a remediation program that offers assistance/funding.

I would suggest to find a local meet up in your area to find locals who are actively doing what you'd like to do, listen to the Bigger Pockets' podcasts if you are not already and to figure out what your preferences are (location, size/type of property, price range, desired ROI or cashflow, etc) so that you can start analyzing deals.

Yes, you have to work around tenants need, and I understand them wanting a legit offer with proof of funds before disrupting tenants, but make sure you have a cancel fee in your offer, and refuse to go through if you can’t see it. 

Read a book on how to find and fund deals3.

Hello BP, If all the buying criteria remains the same, which county is more desirible to invest?

It's their responsibility to pay or they can find somewhere else to live...dropping funds at my bank is not that complicated.Definitely get a lease in place...maybe month-to-month until you learn they are stellar tenants. 

Me and my brothers agreed that if we split up and she kept the house we would manage it for her (make a Little money) but also I would fund the next 3 family on my own and they would be partners. 

But I will probably be using a HELOC to help fund it.

These include bank accounts, stocks, bonds, mutual funds, and so on.