When you say "video lagging", do you mean pauses and stutters, or do you mean the video is playing slower than real time, causing their timestamps to fall further and further behind? Wifi cameras from 2009 are almost certainly streaming mjpeg, which is a huge bandwidth hog and is typically done without any kind of buffering to guarantee smooth streaming. If your wifi is overloaded at all, this would be cause the streams to pause, stutter, or simply run at a lower frame rate. Live mjpeg streams do not usually fall behind by more than one or two frames in bad network conditions; they just get very choppy.
If you upgrade to modern h.264/h.265 cameras, even with their much better compression ratios you are probably going to end up using even higher bit rates than your old mjpeg cameras. It may end up performing even worse. For good results, do not use wifi for anything that has an RJ45 jack.
