Deed of Variation - Right to Apply for Grant

I am seeking assistance in a matter where I have been instructed by the nephews of an intestate aunt.

The aunt died last May and was survived by my clients’ father ( sole beneficiary on intestacy) who died a few months later leaving a Will appointing his partner and thereafter solicitors as executors and leaving his residuary estate to his partner. The partner is therefore entitled to take take out letters of administration and benefit from the proceeds of the aunt’s estate but has stated she wishes this to pass to my clients and for them to deal with the aunt’s estate. Had my clients’ father not survived the aunt they would have been next entitled on her intestacy.

Solicitors instructed by the partner in relation to the father’s estate have prepared a Deed of Variation signed by the aunt which includes a Notional Will appointing my clients as executors and leaving the aunt’s estate to them.

My understanding is that the appointment of executors in the Deed is invalid but the variation of the entitlement to the aunt’s estate is valid. I am unsure if this will be sufficient for my clients to apply to the Registry or whether a Deed of Disclaimer from the partner would be required and in addition if the Deed of Variation is to be relied on then if any renunciation of the right to apply for administration in the aunt’s estate is also required from the partner and solicitors as executor and substitute of the father’s Will?

Any advice would be very much appreciated.