Chan, Eric's tip is gold.

Make sure any flips can carry themselves if you have to hold them. 

I buy or control property using Subject To purchases, Options, Master leases, Joint Ventures, Seller Carried Notes, Etc..... without using a lot of my cash.

Make sure you are carrying lots of liability insurance you will need it very soon.

To add to what I mentioned previously, and the comments above, there are several other approaches to this, aside from your sister becoming a real estate professional, and meet it's requirements, or having you employ her, and as a salaried employee, requires you to carry unemployment insurance, workman's comp, filing state, federal with holding tax etc. 

Nothing fancy but it's very quick, easy and don't need to carry your calculator with you.

To answer questions, if you will.We get paid for our time, which is all we have to sell.We get paid to do the research necessary to answer those questions.We get paid to take on the liability (and carrying the E&O insurance) of possibly answering those questions incorrectly.I don't get charged, nor do I charge, for simple questions that can be answered instantly from prior knowledge.But determining what your tax liability is, if you should sell some properties, could be a fairly complex question to answer. 

Anthony, Carrie is spot on. 

Should I carry insurance on them ?

Except the good ones...treat them as a resource more precious than gold and pay them whatever they want and smile.