If the rules are the same in Scotland as England then...
A potential issue i can see is that if the value of the two places exceeds the IHT threshold, could we have to pay the tax with her husband still in residence (if he is the surviving partner), as we wouldn't have any obvious way of doing this without selling one of the places?
Generally you can transfer any amount to your spouse and there is no IHT due. That might be different if the flat is owned by a business which your mum is the owner of, you would need a specialist advisor to be sure.
I'm not clear where the £570k number comes from.
Does seem odd. Ask the solicitor?
The concern is that we (the kids) would inherit the properties on mum's death but her husband would have the right to the benefit of them. He has not inherited the properties themselves in this scenario, hence the concern over possible IHT falling due.
If the rules are the same in Scotland as England then...
Generally you can transfer any amount to your spouse and there is no IHT due. That might be different if the flat is owned by a business which your mum is the owner of, you would need a specialist advisor to be sure.