Hopefully your brother-in-law has had a TV licence for the past seven years as, even though it was free, he was still meant to get one. i.e. under the system that has operated up until now, people over 75 weren't exempted from the requirement to have a TV licence; they were only exempted from having to pay for it. (It's akin to the system that applies for disabled people in respect of their vehicle tax. They need to 'tax' their vehicle, even though they can do it for free; they can't just drive around in an untaxed vehicle).
The foregoing isn't just a pedantic point because you need to know whether or not the TV Licensing people have got your brother-in-law on their list of people who've currently got free licences. If so, they'll automatically write to him and tell him what he needs to do. (He's not required to do anything until he receives their letter). That basically means that he'll be invited to apply to continue to receive a free licence if he's in receipt of Pension Credit or to sign up to a payment plan otherwise.
However if your brother-in-law really hasn't held a licence at all for the past seven years (which technically means that he's been breaking the law, even though he could have had one for free), the TV Licensing people won't know that he exists and therefore won't write to him. In which case it will be up to him to either apply for a free licence (if he gets Pension Credit) or to make arrangements to pay for one.