First off, I’d just like to say that we certainly don’t try to trivialize anyone’s problem with their equipment. My goal is to see users here on the forum get their money’s worth from their network and internet plan. Unfortunately, and I really believe this is the case here, you are finding out that your devices, specifically the laptop with its single antenna, single data stream card can’t support higher data rates. We have seen this before, on more than one occasion, after upgrading to a higher service plan and expecting the best, a user finds out that the end devices can’t support the upgrade. And, I can guarantee that you won’t be the last. If the wifi card on the laptop was 5 Ghz capable, the easy solution would be to simply abandon the 2.4 Ghz band and use a 5 Ghz network forever and not look back. That would be very simple.
Can you post a screen capture of your parents wifi environment as viewed with inSSIDer? The one thing to remember is that everyone's wifi performance is unique. It’s the result of a combination of factors which include items such as the router performance, mobile device performance, wifi environment including interference from nearby routers and other device such as cordless 2.4 Ghz telephones, microwaves and others. When you mix all of these together, they combine to produce different results for every device.
The fact that you are seeing higher data rates on your parents network would lead me to believe that the wifi environment is different, either due to the number of nearby routers and possibly due to the number and type of devices on the network. But, for where you live and operate your devices, the end results are not the same, ergo, the only way to improve that performance for your location is to use a different wifi card or dongle.
There is one thing that you could check. The CGN3 is not capable of handling a mixed device 2.4 Ghz network and is not certified for it. What that means is that the CGN3 wifi data rates will lock down to the slowest rate device on the network. The CGNV4, ie the CGN3ACR and above are certified for mixed device networks. At least on paper. I haven't seen anyone come back to the forum indicating that they have tested this and confirmed that the CGN3ACR operates as it should. You could be the first to confirm or deny that, but you would have to know exactly what each wireless device that you have is capable of operating at and know where to look to see the connection rate on the device. Say for example you have another device that is capable of operating at 300 Mbs/s. Turn off all wifi devices except that one and confirm via the user interface that it’s actually connecting at 300 Mb/s. Then, fire up your laptop and check both connection rates. The other device should still indicate 300 Mb/s, while yours will indicate 150 Mb/s. If that is the case then the CGN3ACR is operating as expected. If the other device drops to 150 Mb/s for a connection rate, then the CGN3ACR is not performing as it should. The problem at that point is a combination of the CGN3ACR not operating correctly and the wifi environment. What that test might indicate as well is that maybe, just maybe, you have another device on your network that is slower than your laptop, and that is what is locking down the data rate. If you turn off all devices except your laptop, that might also determine the same issue. You would probably have to give the CGN3ACR up to five minutes to adjust the data rates. It should be faster, but I don't know how fast it does respond. Or, you could turn off the modem and power it back up with just the laptop running, in terms of wifi devices. To see the connection rate, right click on the internet symbol at the lower right hand corner of the screen, and select Open Network and Sharing Center. Left click on the connection link that sits on the middle right hand side of the page to bring up the Ethernet or Wireless Status page. The speed that is indicated on that page is the connection rate to the router or modem, not the actual delivered data rate. You can use that to determine the connection rate and, understanding that the connection rate is dependent on signal to noise ratios, know that a lower connection rate will be the result of less than optimal signal strength and signal to noise ratios. Its not exact but it can give you a rough idea, which corresponds to the signal levels that you see with inSSIDer.