While there is a two month period in the case of 2 leaseholders once one says no the process is frustrated. the prudent landlord however takes a risk if they then sell"early" as there is always the risk of a change of tack. LLs wishing to sell "early" need documented surrender of their LH's right to first refusal
I agree it is probably sensible to wait the full two months before proceeding, unless both leaseholders reject offer in writing.
Guess the pigeon will have to wait it out