The work you are describing would normally require a building permit and engineering review. The typical spans and loads characterized below do not substitute for an appropriate review and engineering assessment.
No. 2 STR SPF lumber 2x10 at 12" spacing is rated for a span of 19'-0 assuming typical floor loads 30 live, 10 dead (bed rooms and attics). For a living room you should be targeting a live load of 40 which has a max span of15' 5" at 16" O.C., and 17'3" at 12" O.C. assuming with No 2 lumber. Increase to 17'8" with select 12" O.C. You are kind of on the border on this one. 2x 12 16" O.C. will make the span.