I’m in the middle of creating a new magic weapon for a particular home brew campaign and want to add two spells to the weapon. Where I’m running into a problem is that I’d like to make it so that the weapon can only use one of the spells per long rest. Both spells are lvl3 one is a damage spell the other a buff. I want to make it so the players would have to choose between which they use when. 

How do I make it so that the weapon itself has both spells but only has one charge per long rest?

Only give the item 1 charge per long rest but attach both spells to it and have each spell cost 1 charge. It’s literally that easy.

That’s what I thought. But it’s not recharging on the long rest.

Magic Item Charges are not actually supposed to ever recharge on a Long Rest since items don’t rest. The DDB Devs added that as a janky workaround for items with Actions because they haven’t added Actions to Magic Items yet.

Even if Magic Items were supposed to have charges refresh on a rest (instead of at dawn), a great many Magic Items refresh a random number of charges (like 1d3 for example) and the system has absolutely no way of generating those random numbers automatically. Therefore, all Magic Item charges must be manually unchecked by the players simply by clicking/tapping the red square to empty the box.

Good to know. Thank you