Income from a Lodger not on a rent a room scheme

I am looking to have 2 lodgers in my 3-bedroom property. Because of this, I do not want to use the rent-a-room scheme, as my expenses would be high. As there will be three of us, will I only be able to claim back 66% of the household expenses, such as heating and electricity, on taxes? I assume the mortgage is not an expense I could claim here? Additionally, if I am not able to claim the mortgage as an expense, am I eligible for the Mortgage Interest Tax Relief of 20% of the interest that buy-to-let landlords are eligible for?

HMRC is unable to provide specific or tailored advice through the Online Community Forums and cannot comment on any form of calculation, example or scenario as we may not be in possession of all the relevant information.

The HMRC Customer Forum is for general queries only and is intended to help our customers self-serve. We are unable to provide financial advice or further interpretation of the guidance provided on GOV.UK. You may find the following links helpful:
Work out your rental income when you let property - GOV.UK
Examples of how to work out Income Tax when you rent out a property - GOV.UK
Tax relief for residential landlords: how it's worked out - GOV.UK
Additionally, it is not possible to check individual tax records through this forum. Customers with more complex enquiries often engage the services of a professional advisor or accountant and this may be something you wish to consider.