(Ex/ sisters are both in medical field.

You either need some support posts under that area or someone needs to sister in the joist for more support. 

it’s not mine - it’s my sister’s dog I’m holding for 3 years now.

I've been living here in Shanghai for many years already and currently managing 7 units with my sister (who is stateside). 

My brother in law and sister are currently doing a live in flip in Charlotte where the numbers are crazy and I will say from their experience to be ready for anything and have adequate reserves on hand for issues that you need to prioritize for (I.e. in case an appliance goes out, heat/air go out, etc.).Not doing it personally like I said but from what I’ve seen it could for sure be overwhelming living around it so having that discussion with your girl beforehand as if the property needs considerable rehab you could both be relatively comfortable in part of the home if extensive rehab is required.

If my sister puts in 20% of the property's value , should she get 50% equity and 50% profits ?

Historically we've functioned as Phoenix's little sister: we don't hit the highs of Phoenix but we avoided many of the lows, and our market tends to mirror but lag behind PHX. 

Also most HOA and uppity types like that have no problem with 30 or more stays) so the maintenance is all in house and the other stuff has to be handled by someone else. my goal is to be 90% hands off so I can be in the caribbean with my sister on a cruise and not have to worry.

Maybe your sister could offer to pay a fixed amount of money towards the buyer's closing costs which would cover the flood policy for the first year? 

My good friend's older sister passed away and the heirs did not want the house, i made an offer and it was accepted.