Transferring to your wife (and you and children) will not be considered resale and you will retain all of the VIP Founders benefits. Your in-laws paid dearly for these points. The benefits are significant (as Jan pointed out, including unlimited housekeeping (if they've had them more than a few years, they'll have this)). These are developer points and you will retain your in-laws developer benefits. They become resale when sold or transferred (to a non-family / qualified person).
A word of caution for your in-laws, they are ripe for being scared by the scammers (take this off your hands for the good of your family). Be sure they are aware that if you choose not to inherit it, you don't have to. If at any time they or you choose to get rid of it, there are 'best options' available from Wyndham themselves. They are not going to recoup their original 'investment' and if they (or you) decide you don't want it, be sure to use one of Wyndham's programs to dispose of them. There have been multiple programs over the past (at least) 10 years, each with different nuances. Understand what applies to you (various exit strategy programs include Pathways, Limited Edition, Ovation, Certified Exit). One number you may call (if authorized on the account is 855-312-9040, Mon-Fri, 9am-6pm ET - that answers as Wyndham Cares - they should be able to help you or direct you). They can tell you the options available specifically for these contracts (your in-laws will need to do the calling). They also have an email
wyndhamcaresteam@wyn.com.
If you look it over and decide you can make good use of it, 100% what others have said - put your name on it now (your name on one contract gets you access to the account (and all the points)).
For me, personally, I also felt to need to convince my Dad it was a gift and not a burden. At the time I started managing the account for my Dad/our family, renting was an okay thing to do and it allowed me to offset our maintenance fees and more (I might bet a month of maintenance fees that your in-laws were sold on that 'benefit' - that they could rent, yadayada). At the time my father purchased, salespeople were handing out spreadsheets of the best time to book for the most profitable rentals. Renting is no longer sanctioned (for lack of better wording), you can read lots on here about that. Suffice for this discussion - it is certainly not a reason to want to own or take over this Founders account.
The ONLY reason to own points is to use them for vacations. For any other use of the points you are not getting good value for your money (to pay maintenance, or cruise, or Disney tickets - those are 'better than nothing options' and never a good use of your $$$.
I cannot speak to RCI, I've never used it. That is also an option for offloading extra points. But I don't think I'd want to own Wyndham points for the purpose of transferring points to RCI (for MORE vacations).
Most definitely, if you decide to keep it, get on the account now. No harm and it lets you start learning. Personally, I feel very comfortable that I can get out of this without personal financial risk (worst case giving it back to Wyndham (and I still hear my Dad in his most syrupy and sarcastic voice saying "isn't that nice of them")). IMO you are not taking on a huge financial burden as you will be able to get rid of it (I would guess with a Wyndham exit program) in 6 months or less (so you are risking paying about 6 months of maintenance fees to cleanly get rid of it if/when you decide to)).
I can't speak to inheritance tax on Wyndham, my Dad's was in a trust and I am the successor trustee - easy peasy for me. For other (non-Wyndham) inheritance issues, I found income for beneficiaries is taxable for certain amounts due to an estate being in Nebraska (we are one of the few states with an inheritance tax (grrrr)). My Dad's estate was in Florida and thus no inheritance tax there anyways. This estate stuff gets super complicated and you need a lawyer and an accountant to figure some things out.
Wyndham can be challenging to get reliable information from. Anytime you can get something in writing from them, do so. My mantra - do your research, make the best decision you can with the information you have, and hope for the best. (I almost used Ovations to change ownership a bit and didn't because they couldn't definitively tell me if my current reservations would be cancelled).
And anytime your want to run your thoughts, ideas, or questions by this group, I highly recommend it. As you can see, lots of opinions and (free, lol) advice! Welcome!