Let's bring down Comcast one dissatisfied customer at a time.

Comcast's prices for any single service tend to be higher than their bundles, so depending on who they talk to at Comcast, they might end up spending less keeping the Comcast TV. Something that a lot of people don't know is that due to the Federal http://en.wikipedia.org/wiki/Internet_Tax_Freedom_Act, in the US, you generally don't get charged tax on Internet service. So, if you get just Internet and nothing else from your cable company, it's usually tax-free. If you get TV and Internet, you start to pay franchise, local and state taxes on the service. It you get TV, Internet and phone, you pay even more in taxes (primarily due to the FUSF tax). Depending on the locality, an Internet-only plan that on paper looks like it costs $10 more per month than the same plan with TV or phone services added on may actually cost the same or less in the end than the bundle due to the generally heavy taxation on television and phone subscriptions. The Internet Tax Freedom Act is really quite awesome.

https://www.amazon.com/gp/feature.html?docId=1002997141 if they sign up for Sling at $20 a month. This new streaming service, owned by Dish, will get them twenty-ish live streaming channels. Add Hulu and Netflix for $10 a month each, and their bill is $40 a month for a wide variety of streaming and on demand options. The Fire TV Stick is also easier to use for non-techies as it has a remote and a central GUI, rather than needing to be launched from a mess of separate phone/tablet apps.

If you do go the firetv stick route, check out http://www.tvaddons.ag. With a http://www.jocala.com/adbfire.html to set it up quickly and painlessly, and a https://www.youtube.com/watch?v=IX7JBDX8Qb4(combined with the tutorials on the tvaddons site) you can change an icon on the homescreen to launch kodi, and play literally anything with those addons. My entire media setup now is just the bare internet comcast package, a firetv, and kodi+those addons. It gives me netflix, hulu, amazon instant, etc and everything else they don't carry. Yea, it's a pirate/"illegal" option, but it's not like torrenting where you can get busted for sharing. It just accesses stuff on offshore filestorage/video streaming sites and pipes it through a nice interface on to your tv. The worst case scenario is that a link doesn't work and you select the next option for playing that movie/episode of that show. I've installed this for multiple friends, including some VERY tech illiterate folks who just jumped straight in to the deep end and love it. It's super simple to use genesis and the other addons it provides(they basically work like netflix, with a bit of fiddling once you pick an actual show to play specific episodes). I found it so damn handy that i bought an extra android box to carry around with me on trips/to friends houses just to play stuff with. The firetv stick is massively the best bang for the buck as far as streaming players go, and that software is the coolest thing out there right now in my opinion. Combine the two and it's a serious game changer. I haven't had something so massively change the way i consume media since bittorrent became popular over a decade ago, or when netflix streaming first got a strong selection...

We just call comcast whenever our promotional rate is about to end and inform them that we would like [new promotional rate that is currently advertised for new customers]. Customer service won't do it but they immediately transfer you to a "customer retention specialist" who had more authority. They will try very hard to get you to buy a package you don't want, but they will ultimately give you what you ask for. It sucks but it's worth doing it for the savings.

All of those devices can share one Hulu Plus account; in my experience they can even run Hulu simultaneously. For Big Bang: if they really don't want to deal with DVDs, they can purchase entire seasons on Amazon Instant Video, which presumably would stream through their Roku. It'll be more expensive up front but then they can watch whatever they want. (DVDs would be cheaper, for the record.)

*cough* project free tv *cough* also maybe chromecast ($35)

Don't misunderstand: the Fire Stick does not need a mess of apps (like Chromecast does). It has its own GUI/menu and a remote. Highlight the thing you want and click. https://www.youtube.com/watch?v=3Dl3xoCKdVM

Seconding gatorae. The problem with being a cordcutting advocate is that if you help someone do it and they're not up to speed on all the tech and resources needed, you will become their tech support. For a good chunk of the TV-loving public, once you get beyond Netflix/Hulu/Amazon this is still the wild west.

One thing to keep in mind is that, as people pointed out above, Comcast can get very flexible with their pricing if you threaten to cancel, but also that your brother and SIL will still need to get internet from someone for any of the TV alternatives above. Comcast's prices for any single service tend to be higher than their bundles, so depending on who they talk to at Comcast, they might end up spending less keeping the Comcast TV.