Freeholder requiring reimbursement for administrative costs

Other

I am incurring unreasonable amounts of paperwork in trying to uphold my duties as a Freeholder in a 2yr dispute with the Leaseholders.
The Lease stipulates I can claim expenses "reasonably incurred in and about the maintenance and proper and convenient management and running of the building".
Can I write giving 30 days notice that letters other than for Ins./Ground rent will be charged at a stipulated rate?How much could I charge and would a letter from me suffice?
The Leaseholders are non occupants of their property which is empty and derelict and have no intention of being reasonable.I need to make sure I address this in a watertight fashion as they have funding for Court and as a pensioner and now a reluctant Landlord [forced from my home]I don't.At the moment boundary fences are down /the garden is a health hazard ,the Council say it is my responsibility..... and the Leaseholders are playing games with me. If I must waste my time and energy I need to invoice it?
Thank you,hoping something positive comes back,
Sandra Ehlers