Yes, you can allow a family member to be an Account Lead – and can choose whether they have dealing or view-only access. You can’t be linked to more than one Account Lead at once, and only one Account Lead is possible within a linked family group.
One type of account you can’t include in family linking is Junior ISAs. That's because a Junior ISA can be managed only by the parent or legal guardian (the 'registered contact') who opened the account – who will already have full access to it.
To set up linked family access, fill in the Family Linking Form. It will also give you more information on how the process works.