A non-lawyer may think that these terms relate to a rental arrangement. He would be wrong. They refer to the way in which property is owned. If two persons own a house or flat they will own legal title to it as joint tenants - that means that on the death of one, legal ownership passes to the survivor. Note the words “legal ownership”. You can legally own land, but not be entitled to its economic benefit. You might, for example, be a trustee of a golf club and you and your co-trustees will be registered at the Land Registry as the proprietors of the land. But you would have no right to sale proceeds or rental income.
The economic benefit is referred to as the "beneficial interest" as there is technically a trust whenever two people own land - this beneficial interest is essentially what people talk about when they have 'equity' in their house. Two people who own property may be legally Joint Tenants but beneficially 'Tenants in Common'. The legal title will always be held as joint tenants but the beneficial interest may be held in either way.
Another example: Mr Smith owns his house with his wife, and they are both registered as owners at the Land Registry; but Mr Smith may be worried about his business and have agreed with his wife that she should have all the sale proceeds. In legal language they are joint legal owners, but Mrs Smith is 100% beneficial owner. Perhaps they have agreed that they will split the sale proceeds 80% Mrs Smith and 20% Mr Smith. In this case they own the beneficial interest as tenants in common, and on the death of one of them their beneficial share does not automatically pass to the survivor, instead its destination will depend on the deceased’s will or the law of intestacy.
If you are acting as executor for someone who was a joint owner of property the nature of that ownership needs to be investigated carefully,and if necessary you should obtain legal advice to help you in ensuring that the property in question ends up in the right ownership and that the Land Registry’s requirements are correctly dealt with.
One of the main issues which can arise, though is not usually a problem, is that whenever land is sold under a trust, at least two trustees must execute the deed transferring it to the buyer. If this doesn't happen, the buyer risks having beneficiaries knocking on their door further down the line. Where the owners are 'Tenants in Common' the deceased's share is passed to their beneficiary under the will, so a trust exists in favour of that beneficiary. The second person who usually signs is the executor but where the executor is also the co-owner, this can cause problems.