The land is to be possessed by him on condition that he stipulates in the contracts he will make with his tenants that they will be obliged to, reside within the years on the concession he has granted, failing which he will regain full title to the land.
1. 二楼Natefree的意见，我是认可的。如果不去掉逗号，... he stipulates in the contracts ... that they will be oblidged to ... 本身是不完整的。
2. 个人觉得，楼主把时间，放在其他通顺的句子上，收获会更大。
这个句子读起来，就像是为了展示而强行编出来的。
The land is to be possessed by him on condition that he stipulates in the contracts he will make with his tenants that they will be obliged to reside within the years on the concession he has granted ... .
改写成通俗语言，大概是
He will be able the control the land, if he makes a contract with his tenants and insists in the contract that the tenant must live on the land for the number of years specified in the contract.
在英美法系的物权法中，所有权和占有是分离的，此人能够和租户签订合同，转移占有，要么是土地的所有人，要么是土地的占有人。
从行文看，占有在未来归于此人被设置了前提条件，就是此人必须在合同中指明与租户约定的租期，并且要求租户在此期间必须居住于所涉土地之上。
可以合理的推测，按照文义，如果此人不在合同中设置此前提条件，则未来无法再次取得对土地的占有。
用通俗的话说，你和租用土地的人签了个合同，如果你不在合同里要求对方必须住够约定的时间，你以后就不能控制这土地了。
英美法系之下，合同双方对于合同内容的约定，拥有非常大的自由，但是我自己想象不出会有人这么约定的世纪情景。这就是为什么，一开始我问楼主这个的出处是哈。
3.即便如此，前半部分依然有分析的价值
The land is to be possessed by him on condition that he stipulates in the contracts he will make with his tenants that they will be obliged to reside within the years on the concession he has granted ... .
The land is to be possessed by him 结果
on condition that he stipulates in the contracts ... that they will be obliged to reside within the years on the concession he has granted 条件
4. 最后一个部分，你的判断是正确的，我也认为需要加and，为了清晰，原因我会在最后说。
为了理解failing which，肯定要先弄清楚which指代为何
然而，但从行文来看，存在着几种可能性
a. The land is to be possessed by him... and failing which he will regain full title to the land.
他在未来取得对土地的占有 。。。。。。，如果不成，则他取得对于土地的完整所有权。
b. ... on condition that he stipulates in the contracts ... and failing which he will regain full title to the land.
（他在未来取得对土地的占有）的前提条件有二，其一，在合同中约定。。。。。。；其二，如果没有对（租户必须住满特定时间）的义务加以约定，则他取得完整的土地所有权。
c. The land is to be possessed by him on condition ... (the tenants） will be obliged to reside within the years ... and failing which he will regain full title to the land.
他在未来取得对土地的占有的前提，是（他在合同中约定两件事），其一，租户必须住满特定时间，如果租户不这么做，则他取得完整的土地所有权。
从意思上说，abc都说得通，从法律的角度分析，c最后可能。然而，即便从c的角度去解释，后半部分说得通了，前半部分还是如2一样，内容匪夷所思。
最后，如果选定c这个角度进行解释，那么，合同的约定部分，本质上是
... he stipulates in the contracts...
they will be obliged to reside ... (and) ... he will regain full title to the land.
可以明显看出，这是个简单句，不能只用逗号分隔
5. 楼主是学法律的还是学英语的？为啥会看这种和物权法相关的句子？
无论是啥，你们学校的英文阅览室，大概至少会有泰晤士报或者纽约时报中的某个，里面有大量高质量的句子可以进行分析和模仿。
还是那个意见，没有必要为这种生搬硬造的句子浪费时间。
