If there's no brood in the hive, then you've been queenless for 3 weeks or more.
Your
syrup feeding may also have started a robbing frenzy. A queenless hive isn't likely to defend against robbers.
A broodless hive this time of year doesn't have much chance of making it through winter. If it's also queenless, there's a small chance they could have raised a queen. If so, it might get mated and lay up some brood yet before winter. However, unless the hive is really strong it probably doesn't have much chance of making it.
The most important thing you need to do right now is stop the robbing, as I assume that's what's happening. First think in the morning I'd screen the entrances to your hive so that no bees can get in or out. If you see bees pile up at the entrance trying to get in you know you have a robbing problem.