People are forgetting to mention one important thing with Demat form. The only big broker using Demat form is Zerodha via Coin. No other big broker is using it. When the mutual fund regulations came in - Discontinuation of pooling for mutual funds and how it affects Coin look at all the problems people had and for how long. Even basic features like auto SIP didn’t work with Coin. Even now SIP with secondary bank accounts isn’t live.
Most other brokers like Kuvera fixed all these issues in 1 month. For most people on Kuvera there were basically no issues even. If you are in SOA form you easily migrate your account to any other broker just by entering PAN number. So if there are issues with Kuvera no problem you can migrate to Groww, direct AMC, MF Central, INDMoney, MF Utilities (king of MF but really old and bad UI) or basically any other broker as most are SOA form. With Coin the process isn’t easy and is also not really cheap - How to rematerialise mutual funds?. As you basically have to convert the units to SOA form.
I would say go for Kuvera unless your father also invests in stocks and wants a combined portfolio but even that can be achieved with Valueresearch.