Light rehab only too, as I'm trying not to break the bank. 

You would get a EIN/Tax ID for the trust and use that to get a bank account opened for the trust to hold the funds and deploy capital as needed.

Buy 3 single family homes ( around $40k-$50k each) and then do a HELOC to get 3 more houses and continue with the snow ball effect.Or ask to a investors bank for a bigger loan using those $120k-$150k as down payment to buy rental properties of course.Thank you!

A bank is going to look at appraised value. 

I'd say the bank.

Is this legal to have a family member buy your properties.Also... my Dad would also be "the bank" for the purchase of 2 duplexes-- let's say.

I am interested to move forward with a HELOC offer from my local Bank here.

I've been using the rental income to update the property so I'm also not banking anything at this time so a good refi will be very important for my potential next deal.

Another reason I like apartment complexes any vacancy does not usually hurt you like it would in a residential multifamily place would.Some Private Lenders will also lend to you including any repairs but I understand the importance of using a Bank to get a "house hacking" loan and its low down payment.. 

I'm thinking about moving from the current property manager due to various issues with transfer of rent and lack of communication so this would likely involve some work in dealing with the current tenants and getting keys from the current property manager.I would very much appreciate any recommendation.