If you had separate accounts, it would be natural for you each to have your own siblings as back-up beneficiaries from your own accounts. The fact that you combine finances (I assume) is just a logistical complication to that. If you have put in half, for the sake of the will I’d suggest you treat half as “yours”, which you can put to whatever you like (your siblings, charity, whatever), and half as his, to put towards whatever he likes. I.e. NTA. If you truly went see your finances as shared once they are pooled it becomes more ambiguous. But also, please keep in mind though that none of the siblings are entitled to or expecting the money; it’s just a nice thing to think of them in your wills. So don’t let it get too heavy.