Account ClosedBigger pockets provides great resources in their "tools" section, I think there is a document titled "Promissory note"You can also talk to any lawyer or a simple google search would do.More than the note, however, it is important that the two parties (lender and borrower) trust each other and live up to their commitments.  

Does anyone have recommendations for lawyers who are specialized in tenant/landlord issues, especially familiar with Hudson county: jersey city, west New York, union city, and north bergen? 

Now you will have to talk to a tax professional and a lawyer about how this truly benefits you but it was explained to me as a major benefit.  

One, my lawyer told me that we can't put her name in the contract because the Seller's attorney and lender won't allow it.

Of course check with your lawyer as well. 

Around this time I was working on some professional (my 9-5 job) things and there was some family drama (it involves lawyers, so I'll avoid talking about it here), so I was distracted.

Have the lawyer send her notice to terminate her actions immediately.Be prepared for any contingency including her moving out on you.

Do we go to the lawyer first and after contract is signed do due diligence?

My  lawyer forced the contractor to get a lawyer to respond to him.  

These tenants will end up being multi-generational and have no intention of ever moving out.I hired a lawyer and very delicately brought up the subject of a buyout.