If it was me I would evaluate all the options then make a decision to replace the burners in the current unit or the whole system. I used to manage a few duplexes and we used Tranes that were maintained twice a year. I think most of them went twenty years or so. These were not heat pumps but natural gas furnaces and it was usually the AC side that failed before the furnace.

I think with new heat pumps you may be able to eliminate the dual fuel or at least sustainably lower the temperature that the propane kicks in.

Both Lenox and Trane are good companies. I would talk to both contractors.

Let us know what you find out.