Hi shygirl,
Pretty much as feisty has said. When I purchased my croft the CC did not have to approve me but you must register the new ownership with them. Apparently it's a criminal? Offence not to!
The expectation and indeed obligation is to tend the croft and use it. Sadly many don't and whilst the CC have a renewed commitment to deal with owners of neglected crofts I think that's a long and slow process to go through.
Owned crofts are certainly heritable, my kids would be most upset if they were not. I'm not so sure about tenented though.
Lots of people run a mile from taking on a croft because of the obligation but I am of the opinion that if you want to live in Scotland and follow the smallholding lifestyle they are a great option. Prices are still quite reasonable and you have a real feeling of history and belonging being a crofter.