The reason for the difference in your scores is the result of the creditors not reporting to all 3 bureaus. This is why lenders pull a tri-merge credit report and use the middle score.
Just a couple of quick points here.
If you can not be "approved" through an automated underwriting system due to your scores, you'll have to go through a "manual" underwrite and that's going to mean more restrictive guidelines which can make it more difficult for you to qualify.
With lower scores, you'll be limited to how many lenders you can work with and you'll probably end up with higher fees and rates.
The best approach is to have a mortgage professional pull and review your credit report to see what can be done to raise your scores to at least a 620.
There are ways to increase your scores in 2-3 days through rapid re-scoring so it's not necessarily a long drawn out process.