I assume this is an english case. If so, the disgruntled beneficiaries can apply under s116 Senior Courts Act 1981 to the Probate Registry to have the named executors "passed over" and the Grant made to either a disinterested party or up to four of the other residuary beneficiaries.
However, this is not a discretion which will be exercised lightly. To be successful you must show that the relationship between the execs and bens has irretrievably broken down or that there is another good reason why they ought to be removed. It might be that they will behave themselves until they've got the Grant. However, if things do start to go awry after the Grant you can apply to the High Court under s50 Administration of Justice Act 1985 for their removal. The s116 procedure is relatively simple and cost effective, it being commenced in the Probate Registry by Summons. The s50 procedure is full blown HC action and therefore can prove expensive.
Removal is not the only option though. Under the "self dealing" rule they cannot be both the seller and the purchaser of the property since they are in a definite position of conflict. If they did "buy" the property, the sale is voidable at the instance of the beneficiaries.