I always enter 100% on the person whose SSN is on the 1099, then "Nominee" out the amount reported by the other owner.

Sch B items are shown on the 2nd page of the Sch B entries, Section E for interest and Section D for dividends. Capital gain divs are a little hard to make sure you get right.

1099B is harder, but I enter 100% and enter a second dummy "sale" to remove the profit/loss belonging to the other owner reducing this owner's gains/losses.

This is for the person whose SSN is on the 1099; the other owner just reports half of everything, since the IRS cannot look up their income.