Borrowing Money for First Investment

[Account Closed]

Hello,

Thanks to all the great knowledge found here and elsewhere we are close to purchase our first investment property (a duplex). Initial we were going to use a mortgage to purchase the property but my mom offered to act as the bank in this transaction. She trust me and I trust her however we want to do this correctly. What would be the best way to go about this? The goal is to make this agreement as solid as possible in case something happens to either one of us the agreement will live on. 

Also we discussed in 5-10 years me buying her out with a mortgage so I could extract the equity for another purchase. Would this be difficult? would it essentially just be like acquiring another mortgage? how long would this take? Is there another way I can keep the money I owe her easily accessible in case I need to do early repayment like a Heloc?

Thanks,

Jake