I think you've mentioned you fly out of BDL? Hawaiian operates direct flights to HNL from BOS and JFK.
The HawaiianMiles MasterCard is the same card issued by Bank of Hawaii through Barclays. Would the personal card be your first personal card with Barclays? There is also a business version of the card. I can't predict approval odds because Barclays be cray cray, and lenders are tightening credit card lending generally. I will say that the 50,000 offer you're seeing is
low compared to recent offers of 60,000 on the personal card and 70,000 miles on the business card (search DoC for an idea of historic offers).
I'm not going to say the HawaiianMiles card is bad, but it's not great at earning
a lot of HawaiianMiles to fly a family from the East Coast to Hawaii and back, especially because of the current low SUB and since Hawaiian devalued their award charts last year. However, when flying Hawaiian, the HawaiianMiles card is a great card to have open. SUB aside, holding the HawaiianMiles card gives you access to discounted economy flight awards. Being a HawaiianMiles cardmember also lets anyone transfer their HawaiianMiles into your account for free, which makes it easy to pool points with the cardmember who has access to the discounted award fares. There's also your first bag free if you pay for your flight or taxes on the card, and a companion fare discount for cash fares (but the point is to try to use miles, so that latter benefit is negligible).
Since your trip isn't until summer 2022, I would keep Hawaiian as an option and focus on earning a flexible currency like Chase UR, Amex MR, or even Citi TYP in case you find a better deal on other airlines. Hawaiian offers a great product and you can really feel the Aloha spirit once you step onboard (several blogs have reviewed the BOS<>HNL flight and JFK<>HNL should be similar, to give you an idea), but they're not always the cheapest cash- or points-wise. If you think there's a good chance you'll be flying Hawaiian anyway, I'd recommend earning as many Amex MR points as you can (not a bad idea in any case) in the next year since MR are still relatively easy to earn a lot of, MR transfers to HawaiianMiles, and Amex typically runs a 25% transfer bonus once a year. Get the HawaiianMiles card when you see a better, elevated offer for the SUB, but really for the ability to pool points when you're ready to redeem for discounted award fares (even better if the stars align and the first year AF is waived).
Hawaiian's site is wonky as I type this, and your planned trip isn't until 2022 so I can't possibly check the number of miles required. For reference, here is Hawaiian's current award chart, one-way, HNL to/from the East Coast:
https://hawaiianair.custhelp.com/app/answers/detail/a_id/2218/~/hawaiianmiles-award-chart#naec
Hawaiian opens their seats for sale 330 days in advance of departure date. There are no blackout dates, but award seats are always subject to inventory. I've also seen Hawaiian hold back award availability for several weeks/months for peak travel times (usually the two weeks around the holidays). While flights tend to be at their cheapest at release, that's not always the case and cash/miles fares can go up and down (use the chart as your guide). Unfortunately, Hawaiian is not like SW where you can easily rebook to save some points.
You can see that Hawaiian has a dynamic chart for award seats based on inventory and demand, so a one-way main cabin economy award fare can range from as low as 30k to as high as 130k (discounted to 26,250-110k for HawaiianMiles cardmembers and elites) miles. You'll typically find the better deals are for midweek travel. Still, that 50k SUB (even in 2-Player mode) won't get you very far with Hawaiian.
This is why if Hawaiian is a possibility, you should start accumulating Amex MR. Earning MR, in general, is a good idea because it's a very valuable and flexible currency, with a lot of solid transfer (particularly airline) partners, as well as cash out value; and Amex is still approving folks for a lot of their cards so there are lots of cards and opportunities that'll let you accumulate a lot of MR in a relatively short amount of time, especially in 2-Player mode with cross-supportals to elevated welcome offers.
MR transfers to HawaiianMiles 1:1 normally, but Amex runs a 25% transfer bonus to Hawaiian once a year making the conversion 1:1.25.
- In 2019, it ran from about 9/23 - 10/7
- In 2018, from about 6/12 - 6/26
- In 2017, from about 6/7 - 6/21
- In 2016, from about 6/6 - 6/21
- In 2015, from about 12/8 - 12/21
If you can accumulate enough MRs in time to take advantage of a transfer bonus to Hawaiian, you could give your MRs a 25% boost when transferring to HawaiianMiles. (However, note that when transferring MR to a domestic airline's frequent flyer program, Amex charges a $0.0006 per point fee, with a maximum fee of $99 to your card account.) Pair that with discounted award fares from holding the HawaiianMiles card, and it's not a bad use of MR points.
If you want to read more, I've replied about HawaiianMiles and their credit card offerings previously. Just do a search for HawaiianMiles and Lain.
Hope this helps.