Lennox VRF dual fuel system control and outdoor unit defrost issue

I have a dual fuel ducted heating system for a 2500 sq ft home in northern NV. The equipment:

• Lennox VRF heat pump VPB060H4M-3P outdoor unit, C35 indoor coil
• Lennox Gas Furnace ML180DFE (propane)
• Nest Thermostat

My issues/needs: The 2 HVAC companies near me have not been able to fix these problems

• The outdoor unit freezes hard when demanding a lot of heat (sometimes vibrates and shudders before the system decides to defrost)
• When I try to fore the furnace to come on by turning up the thermostat by 10-degrees, it does not come on (I was told this is a work around)
• Given my cost of electricity vs propane (I have PEV panels) it makes way more sense for me to run the heat pump down to 10 degrees outside temp
• I want a thermostat which allow me to manually switch between heat pump and gas furnace and ideally let me change the balance point (I know I can do this on the outdoor unit).

I've been told there's no way for me to manually control what I have — even with a new Lennox thermostat? Why does it defrost properly sometimes but not always?

I'm very handy person and could install a new thermostat, flip din switches in control boxes, etc. to DIY a fix because the pros around here are nice but not helping. Help please!