If this is a home that best suits your family needs, the first thing I would do is pull your personal credit report to ensure full accuracy. Then, I'd contact several banks speaking to mortgage experts explaining your situation that you need x amount of money for a home and tell them of the obstacles you face. Then ask them if there's a program to help you with free credit repair or for a referral to another company/person that can help. The golden answer you're looking is how long will it take you to qualify for the loan amount needed to secure the property.
Once you have this information, I'd submit an offer for owner finance with inspection contingencies, a little bit of earnest money, and the terms (down payment, interest rate, who pays 3rd party fees to collect payments from you/distribute to the owner, term used for payment, how long you have to obtain other financing, balloon payments etc. Then I would provide as much information about yourself that you feel comfortable sharing as an addendum. I'd submit a letter explaining why you want to purchase the home, how it fits for your family, rental history, work/personal references, information from the lender explaining the time frames for you to obtain your own financing. When you're faced with what to share, just ask yourself what would provide peace of mind to the seller signaling you're a legitimate person that will take care of the property with a plan in place to obtain your own mortgage in the future.
As far as the realtor goes, I would find a different agent that has experience in drawing up owner financing deals. The contracts can be quite complicated, and you might seek legal counsel in drafting up a specific one to meet your needs. Be aware you might have to pay higher interest, more than the property is worth (in 2 yrs when you obtain financing, sometimes the seller wants to hedge against the appreciation by asking for a higher purchase price now), and fees you don't normally encounter in a bank financed transaction. Be prepared to negotiate all the terms knowing paying the 3rd fees vs. a 1/2% interest might be the same amount of money at the end of the month. The more familiar the realtor is with the process, the better off you'll be.