On conjoining reading of your query and your subsequent explanation, it is understood that the portions of the property were separately allotted to the sharers by way of alleged settlement deed and so the word " so and so sharers entitled so and so portion" was incorporated therein.
Therefore, though the deed is named as settlement deed, it can be treated as deed executed for recording partition effected between the sharers. Hence, the sharers are entitled to alienate their share as their will and wish.
Moreover, even if the property is not partitioned, there is no legal restriction on the part of sharers to sell out their undivided share of the property. The purchaser can claim partition in the place of vendors/sharers inrespect of the vendors entitled portion.