Sorry to read about your son. The advantage of a SIPP is the tax contribution on the way in but Ben has mentioned she has to have earned her own money to take advantage of that tax benefit, so unless your wife can take advantage of unused allowance for the past three years you may be better off looking at an ISA. On the ISA as you’ll know there is no tax benefit on the way in but there is also no tax charge on the way out either.
You’ll also need to consider how you manage the pot, whichever wrapper it’s in. I’ve not seen anything from Freetrade on allowing customers to manage other portfolios, maybe it’s not been an issue yet as there is no JISA. Also how actively are you going to invest and will there be regular contributions?
The stocks you mention are likely to continue to do well and may be candidates for a “coffee can” portfolio but I’d be more likely to look at Investment Trusts and fill any gaps from there with specific stocks rather than start with them. I’m also a bit unsure of Paypal as they start to charge a fee for inactive accounts, though that may be more a greed than struggling thing.
Fundsmith, Scottish American, Scottish Mortgage, Worldwide Healthcare, Merchants and the like are decent ITs, though that would need Plus and I’m not sure I’d want to spend the £10 + £7 to get a Plus SIPP in this scenario unless the pot was healthy or being contributed to. £10 for Plus and an ISA may again suit better.
Could be an opportunity for FreeTrade to give discounted products to carers or stay at home parents, would line up nicely with their aim to get more people investing for their future.