You're almost there. Yes all the lines on the 1040 are for both of you combined. Line 4a & 5a is the gross distributions from 1099R line 1. Except if 4a is the same as taxable amount on 4b then 4a won't be filled in. Same for line 5. The IRS says in the 1040 instructions......Except as provided next, leave line 4a blank and enter the total distribution (from Form 1099-R, box 1) on line 4b.
It's also possible for line 4a or 5a to have less than line 4b/5b if one of the 1099R gross and taxable amount are the same. That might be confusing so just ignore it.
