I have two three-way switches in one box at the bottom of the basement stairs. One switch is for the stair light, and the other is for the basement lights. Both of these are the "second" switch in their circuit. What I mean by that is (hard to explain in writing) that the hots enter the "first" switches upstream of this box, the travelers run from that box to this one, and then the lights are at the ends. Since there are two separate circuits, should the neutrals and grounds be tied together (as they usually would be) or should they be left separated?