My husband's mother told him to get a prenup.
We had our own assets before marriage worth the same amount each and earned the same salary.
I laughed when he told me her suggestion and reminded him I wasn't forcing him to marry me.
We married without a prenup.
In terms of your situation, you need legal advice as your assets are joint with family, it's a bit more complicated. You also have to consider your gut feeling about him. None of us know him, and being offended at the suggestion of a prenup is not a red flag in itself (I was offended when suggested to me, but my reaction was to laugh). Anyway, no alarm bells from this post as we don't know anything about the DP. Some people absolutely are offended at the suggestion despite not being gold diggers. It can be insulting because they may feel you are not invested in a forever marriage etc.
I really am on the fence with prenup suggestions in general, as I said, I was offended, but laughed. I knew I wasn't a gold digger, hell, I ended up earning twice his salary after we married and now I have assets worth a lot more than him. No prenup, and hoping we have a forever marriage, and if that didn't happen, would really hope we could be amicable when dealing with financials.