Here's some tips or things to think about
Firstly where did he have the bitcoins?
On an exchange? eg Coinbase, Kracken, Binance, Gemini are all names of exchanges. If you have access to his email, go through it and see if you can find any emails from those or other bitcoin providers. If you can, get in touch with them directly. I know Coinbase has procedures for next of kin accessing accounts, and I suspect the others may as well.
On a software wallet (like exodus, and there are quite a few others). Go through his computer and search for a "wallet.dat" file. If you have that, you have the bitcoins. DO NOTHING FURTHER FOR NOW. The bitcoins are safe, they arent going anywhere, dont do anything in a rush.
On a mobile wallet (like Mycelium and there are a few others). Unless you can directly access the app (usually with a password), you need to find the seed phrase (see below).
On a hardware wallet (like Ledger or Trezor), If you can find a hardware wallet (google for what the two above look like, there are others, but only hardcore bitcoiners would go for the more obsure ones), these can be accessed by a pin number - typically 8 digits. If you know what he might use you can try, but you risk getting locked out if you put the wrong one in more than twice, so only try once.
If none of this helps then you are looking for either
- a seed phase - this will be 24 or 12 random words, the order is important. It would typically be kept on paper, not digitally
- or a private key - this will look like a long string of random alphanumeric digits.
If you have either of these you have the bitcoins.
If you do find a seed phrase or a private key. Do not do anything in haste. The bitcoins are safe and they arent going anywhere. In particular.
- Do not put it into a computer until you know what you are doing
- Do not share with anyone, ESPECIALLY randoms on the internet
- Do not take a digital picture of it.