Well the simple answer to the CGT question arising is that each daughter will have a potential liability to CGT based on a proportion of the number of months that your house is not their principle private residence divided by the total number of months of ownership between 1997 and any date in the future when they cease to own it.
In other words, moving into it will not completely remove a liability to CGT assessment for each of them - it works in proportion to length of times occupied/owned.
There are several twiddly bits that could be added, like the final 18 months of ownership period are always discounted in any CGT liability calculation, one or both daughters may wish to elect the property as their 'principle private residence', but there are rules attaching and it would depend on the situation regarding their current home ownership.
None of what I have said impacts your IHT position, only their future liability to CGT due to ownership.
You might wish to take paid for tax advice to minimise this for the whole family - it doesn't look the decision to shift ownership to daughters in 1997 was all that clever, and it certainly has hindered since the Labour Chancellor changed the rules by doubling IHT bands for couples in about 2007.