sorry for the delay.
You can convert the two to C3 under Class MA, but this would then require planning to go to C4.
Personally I would probably look to convert straight to an HMO, either as one larger Sui Generis HMO, or two.
I would recommend using a planning consultant for this.
If you or your client needs help, please reach out via https://planninggeek.co.uk/contact