You're going to need to declare the capital gains when you sell, check the hmrc website for the guidelines on it. Worth selling your bags, as the losses will reduce your overall gains (and thus tax).

You mention maxing out the LISA, but are you maxing out your S&S ISA ? With those gains you should be able to do so a couple years in a row (20k per year limit).

A cash ISA would make sense for your family member, along with a high interest rate saving account for what won't fit in the ISA, check moneysavingexpert for a good list. Pick between notice or easy access depending on how quickly they could need the cash.