Who lives there now? Who owns it? If the plan is to sell it and split the proceeds then, since it was (presumably) your joint Principal Private Residence (PPR) up to recently then there should be no CGT implications and you both may be able to retain your first time buyer status if the conditions above are met. If you have owned and lived in the apartment for more than a year now and will be receiving some of the proceeds of the former family home sale then there may be a partial CGT liability since your interest in the property may be deemed an investment property one.
2) Would I have to pay capital gains on any gain on the apartment, which was never rented out?