I got a $90,000 inheritance when I was 23. Obviously a completely different time in my life than you are in, but this is how I thought of it. I divided it into 1/3's. Spent 1/3 on going back to school to become a nurse (basically 2 years of living expenses. Damn lifestyle inflation!) 1/3 on a downpayment for a house, and put 1/3 in a retirement account, that I recently cashed out to use for downpayments on rentals.
There are several moments in my life when I felt my mom was giving me a new gift, when I bought my first house, and everytime I have sold or bought a house since. Also, when I cashed out the retirement account. It's a good feeling, like she is still here, taking care of me, loving me.
I would use part of the money in a way that feels like a gift from your father-in-law to your husband, whatever that is. That doesn't have to mean in a wasteful way. It could, though. For instance, since you already are in a great starting place, maybe you could use some amount for something fun - whatever that looks like to you. Use it to fund a vacation that takes place on your husband's birthday. A $300 camping trip or a $3000 cruise, whatever sits best with your family.
It's nice to have some symbolism, though. And a way to keep it seperate from your other money, so everytime you do use it you feel the connection.
Heidi