I've been there with my DSLR struggling in low light too. It's frustrating when you're trying to capture those family moments and it just won't lock on. What helped me was switching to manual focus for those tricky spots and just twist the ring until it looks sharp in the viewfinder. Works great.
Also and make sure your sensor isn't dirty, that can mess with focus. Give it a gentle clean if you can, or take it to a shop before your trip. And yeah, bumping up the ISO a bit lets in more light without blurring everything. Fixed my issues last vacation.
