Building a family time capsule is an activity that the whole family can take part in. You can ask each relative, and maybe some friends too, to select something special for the capsule. Ask each person to write a short note explaining what they have chosen and why.
For the moment, this capsule might have to be virtual, but once distancing measures are eased you can ask people to drop off their items to you and you can collect them all together for the capsule.
When you have all of the items in the capsule, you can decide when you are going to reopen it, noting the date on the container and maybe setting a reminder on your phone or computer.
How can I help someone to do this?
You could help to get the whole family involved, spreading the word and helping to collect the items when distancing restrictions allow.