Help!

If they're unsure about the show and/or fandom, trying to force it on them is a risky move that might just push them further away. If they're interested, then this sounds like a fun idea! Sonic Rainboom and Fall Weather Friends I think are pretty good introductory episodes, because they aren't too over the top in getting their lesson across, give a good idea of how each of the mane 6 is, and are entertaining. As for a Pinkie Pie episode, I think Party of One typically is the big favorite.

Feeling Pinkie Keen = best Pinkie episode to show, i'd say.

I agree with Lightning, you can't force it onto them, being a brony comes naturally, and people have different opinions to others, just something to bear in mind.

It's be best not to sit them all down for all this, just watch it and have it going on in the background. That's how I converted my family. I would show them the season 3 premier, because...well, it's a great pair of episodes. But, I converted my family with Lesson Zero and Winter Wrap Up.

I'd start from the first episode...that way, they will see that she show isn't random colours for kids, and won't ask questions like Who are these guys, why are they friends and such. First episode is one of the best too and has Nightmare moon in it.

First off, do your family already know about the show or fandom to any extent? Do they know about the older generations of My Little Pony? If so, what do they think of it? How would they react upon hearing the song? (I'm telling you, if someone else had sat me down to watch the show for the first time, I would have bolted as soon as the intro started rolling).
Just wondering if it'd be a good idea to begin with and without knowing anything about the circumstances, it's impossible to to say.

Well... I'll just trust you on this one then. Hmm, may I suggest Bridle Gossip?
One of the interesting things about the show is the universe and how diverse it can be. There's a lot more to Equestria than just ponies. You have all of the mane 6 involved being themselves in an unusual situation, you have quite the eccentric African Zebra equine Zecora and you also have the goofy Poison Joke gags.

I think that your best bet would be to have two episodes that shed some light on the diversity so make it two "unusual" episodes. Your family should be smart enough to see the similarities themselves, they just might not think about it until someone points it out.

First episode I watched was S01E09 Bridle Gossip. I'd recommend it as a first. Kinda weird when you say "recruit them into bronies." Don't try to force it down their throats.

Yes, lesson zero, best episode because its Hilarious and you see a bear's head snapped xD

Pinkie keen- best episode with pinkie... watch for the tail and the twitches 0.0

...Hurricane Fluttershy XD