The Sony a7iii is a great camera. You need to use the full frame capability. Trade in your old lenses for a Sony lens. I recommend the Sony FE 24-105 f4. It is a fine lens designed to work with the Sony alpha systems and will likely satisfy most of your photo needs. You might consider adapting the 150 - 600 lens you have, but it will be slower than the Sony equivilent if you are using it for wildlife/bird photography. Yes, Sony lenses are somewhat more expensive, but they are well matched for the system and work well. You might consider replacing your four current lenses and buy two Sony lenses as a replacements. It makes it much easier traveling.