As your sister has lived in the property for the entire period of her part-ownership of it, her share of any gain you make will be tax free so long as the property is sold within 18 months of her moving out.
Assuming the property is sold in, say September 2014, by that time you will have had an interest in it for 47 months from late October 2010 of which you will have lived in it for 21. Your share of the gain for that period will be tax free as will your share of the gain for the last 18 months of ownership. That amounts to £24,894 (£30,000 / 47 x 39) assuming you sell it for £275,000. The remaining taxable gain of £5,106 will be covered by the annual CGT exemption of £11,000 and so you should have no CGT to pay.
As for the house you own with your husband, so long as you live in it for the entire period of ownership or sell it within 18 months or moving out, any gain you make will be tax free. This is on the basis that you did not elect for the property you own with your sister to be treated as your main home when you acquired a second one with your husband.
Take a look here
for more information on the main home and CGT.
I hope this helps but let me know if you have any further questions.