Tenant in Common - Probate for death of Mother (2 years before Father)

My mother died in 2020. The estate passed to my Father. He subsequently passed in 2022. My sister and I obtained a Certificate of Probate for his estate. They owned an allotment, with it's own Title Deed - which I am told is Tenant in Common with both of them. 

We are trying to sell the allotment to a neighbour, but the Solicitor is not being very clear about what is required. |

My question is, do we need to obtain a certificate of probate for my mothers estate? 

Is that Probate required by the Land Registry?

With thanks.

Mark - probate is always required if a sole legal owner has died. Whilst land/property can 'pass' to someone through a will/intestacy that's not enough to then transfer the legal ownership.
From your post it's unclear as to which legal title you are referring to and if so who is the registered legal owner
You may find our online assisted guidance a useful resource to work out what's needed to transfer the legal ownership - HMLR Guide: Start - External  · HM Land Registry