you need to follow the procedure for CatOS to IOS conversion
you need to do it two times one for each supervisor /MSFC
so your first step is to remove one sup convert the remaining sup, then you will remove the converted supervisor and you will insert the other one alone and you will perform conversion again for the second supervisor.
At the end you will insert first sup again and you should be able to get one active and the other standby in native mode
at the end you will get a single session to access the device
(2) on CATOS we got LACP configured ; is any modification needed on it
LACP is supported on IOS too but you need to configure it. By the way the device needs to be configured.
There is a config conversion tool but it is not recommended.
follow the document step by step depending on your sup model
HW and SW requirements are listed
it will take some time (hours)
Hope to help