He's your brother, so I'm assuming you've known him all your life and that you grew up with similar financial influences. You should know whether the members of your family are responsible with money, and whether your brother's approach matches yours and your family's. Which makes me wonder why you are asking for internet advice, and I wonder whether you are perhaps concerned about the fiancée who is coming from 500 miles away and "has only a couple of thousand". Perhaps you do not (yet?) know her or like her well enough to want to help provide her with a home? Or maybe that she will lead your brother into living up to or beyond his means? Or that they are spending a lot of money on an extravagant wedding instead of putting it into their future home? Only you can answer these questions.
Personally, if my brother asked me for a loan, I'd give it to him with very few questions asked. But then, I've known and loved my brother for half a century, I know that he is honest, honourable and careful with money, would ask me for a loan only for a good reason, and would pay it back on schedule. Pretty much all I'd want to know is whether I could help with more than money. I certainly value my lifetime relationship with him more than I do a few thousand dollars.
So I think what you need to do is consider your relationship with your brother - which includes his future wife, as once he is married you will be having a relationship with them as a couple. How you feel about that relationship will give you the answer whether to give or loan money, how much you might hand over, and what your expectations are about getting it back.