I don’t care how much money your step father earns. you are asking for $250,000 in loans. If he is a wise business person, he will be drawing up a loan note with a lawyer that includes the repayment plan. You might want to get THAT information before you apply to colleges.
And in my opinion, you should be less optimistic about repayment. If your SD researches college loan repayments, he will see that the usual repayment schedule is 10 years…with the ability to increase that payment time and the interest as well. If he expects a ten year repayment…that would be about $3000 a month for ten years…with just a modest interest charge.