In an attempt to help, I think Brian has done something that could have major consequences. For one thing, I don't think Davey is going to take it well at all. With all his talk about making only subtle changes to the time line, Brian has just made a major change. To Davey, I think he'll see this as no different than taking charity - he'll see this almost as Brian trying to buy him, and he'll resent him for it. In an effort to bring them closer together, Brian may well have created a wedge to drive them apart. Only time will tell.
The thought of Davey's mom having 9 million dollars is also scary. Seeing how she behaved in Do Over and particularly in DOR, she could do some pretty bizarre things. Forget Downey - she might decide to move her family to San Francisco, or LA, or a castle in Scotland. Who knows what she'll do? I also wonder how long it will be before she starts to wonder how a gift ticket just happened to have the winning numbers. She's shown time and time again that she's a smart lady. Pete's even smarter - I wouldn't be surprised if he's figured out Davey and Brian's relationship by now.
The biggest problem with Brian's action, however, is that he did in fact make a major change to the time line. That winning ticket reset the jackpot, affecting the fortunes of thousands of winners after that throughout history. There will be winners and losers from this change - fortunes affected with unknown consequences. This isn't the butterfly effect - it's more like a tornado.
One positive thing - I don't think Brian's parents will doubt him any more.