I'm no exactly new to BP but have never introduced myself or gotten involved. 

There is a ton of trust involved on both sides, but especially when you're the one shelling out the money. 

My husband and I just got our first property, we are using the BRRR method.

Check out the "Enemy Method "You can find videos.

If your goal is to grow your LLC, consider arranging all of your properties under an agreement with your LLC to manage them & take all of the legal steps to ensure that the structure is correct. this may involve creating LLCs in the state(s) your LTRs are in to own the property and your PM LLC managing those properties, so that you don't have a concentration of all of your portfolio in one entity.

Do you have a particular formula or method you rely on to make sure the numbers add up?

What is likely to happen is you try to solve HER problem - just to have it repeat.You really cannot evict one person w/o evicting ALL OCCUPANTS.Know you think you are doing the right thing, but you are NOT.The only way you can/should assist the mother is if she files a police report on the other occupant.If mother is not willing to do this, do NOT get involved!

And don’t pay anyone or sign anything before you get your carrier involved.

If you can get in with a real estate brokerage that is more involved with investors you will learn a lot more.

well, duh.I'd put this in unquoted text but I don't see a method of disabling the quote format in the text editor.They can ask you to serve notice so one unit (or both) are vacant at the time of possession, but if you agree to that make sure you have a large deposit and some of that is not refundable if the buyer backs out as you will need it to cover the lost rent. thank you.