The important thing to do before deciding this is to align the mindset and knowledge about Bitcoin, and in my opinion, couples who have Bitcoin and agree to invest in Bitcoin must have understood at least how to store Bitcoin.
Have the same understanding of how to secure Bitcoin and also the same goal of investing in Bitcoin including if the relationship does not go well so that Bitcoin can still be accessed by both and get benefits from the Bitcoin they have, including it in the marriage contract can be a solution and using multisig could be a choice.
If they are moving past the doubting each other part and already just trying to figure out what is the safest way to invest into bitcoin, then they already achieved so much together. If you consider what would happen when the relationship goes south, then you are already focusing on the wrong part of a relationship.
You can't just focus on what could go wrong, while that is perfectly normal because every relationship "could" end at any moment, that doesn't mean that you should be in a relationship, while thinking about potential of it ending. Go with your gut, and on the way to your gut, check in with your heart. Those two will tell you what's what in between them (love ted lasso). That should make you invest together easier.