That depends on the bikes and components. For road bikes, you should be okay with hanging them any which way you want. If you have suspension-equipped bikes, you will want to dig out the owners manuals and/or contact the manufacturer as some (usually older) suspension forks don't like being inverted or have their oil baths up against the seals. Another component with similar issues are disc brakes which may not take kindly to prolonged inverted positions as air bubbles might end up in the line.