It is very likely that the deeds to the other two cottages contain a similar right, therefore your neighbours would have a right to cross your property to access/ egress their property. An examination of their deeds would confirm this (these can be obtained from the Land Registry, provided the properties are registered).
Therefore you cannot obstruct their right of access.
You can put a lock on the gate for security purposes but you must give a key to the other property owners who have a right of access.
I hope this helps.
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