My sister and I inherited the family home last year. She lives there
on her own, with my agreement as she is unwell. Four months ago, she
met a man 15 years older than her. He was made bankrupt 10 years ago
and proposed to her within 3 months. I now find they have discussed
him moving in and buying me out. The only way this could be done in my
view is by my Sister getting a mortgage on 50% of the property with
payment being made by him renting out his house, which I am not even
sure that he owns. I can see my Sister taking all the risk and losing
the house on subsequent default of payment. His wife died in March of
this year, and I am naturally suspicious, especially since my Sister
and I both decided we would never sell the house.

My question is - What should I do to protect my/our interest in the
house and what can I do if he starts gradually moving in to the house,
which appears to be happening.

Mostly I'm a land law ignoramus, but some relevant points might be:

- if she mortgaged half the property (a lender might not wish to enter
this kind of deal anyway), and he contributed some of the repayments,
he might create an equitable easement enabling him to live at the
property. However, simply him having permission to live there from
your sister, and any contribution to repairs etc might create this in
any case.

- BUT, there's very little to stop your sister severing any joint
tenancy you might have and simply giving all or some of it to this guy
anyway

- It would be difficult (but probably not impossible) to force you to
relinquish your half share

- You can (and probably should) register your right to live in the
property

These are skimmed from my undergraduate legal knowledge, and may well
be incorrect or out of date. I do however think that you should
receive independent legal advice from a solicitor SOON. Before doing
so however, consider what your goals are -

 - Do you want to stop this man from marrying your sister? You
probably can't, and shouldn't.
 - If she does, are you adamant that they shouldn't live as a couple
in the house?

The fact is, if you don't want the house ever to be sold, but you
don't live in it, and you don't want your sister and her prospective
husband to live in it - just exactly what do you want to happen?

Co-ownership has a number of flaws, ans especially where it concerns
one is living in the site, and in "control" of maintenance, utilities,
upkeep, taxes, etc., since the 50% is a true ownership right, then
there must be some inherent value assigned this,..and as such, despite
well-meaning, well-intentioned concerns on behalf of both parties,
then an agreement should be contractually entered while still
possible. It is generally reasonable to say that "appraised" value is
an amount determined through a third party, and amenable to both
parties, and it should be decided, between the co-owners that any
alteration of status which affects either the property or the
co-owners would require either a complete appraisal, determination of
value and re-articulation of the contract ownership, OR, a prenuptial
aggreement that no alteration of pre-existing co-authority will be
altered by marriage or status.

Now, this is not the most beneficial offering to both parties, as it
impels the caretaking member of the co-ownership to either count on
the other party to co-fund or apply maintenance and upkeep as a
value-added asset. If this is not done, then the maintenance is
forfeit by the caretaker, and the co-owner retains full 50% ownership.

Conditional ownership, meaning that one party keeps and maintains full
or partial upkeep, and contractually agreeing that no third party or
status change in EITHER party will deny or preclude any rights of the
other will have to be done separately from title and inheritance
status, due to marriage rights, etc,... and needs to be signed into by
ALL parties involved (pre-nup by potential husbands, or existing
arrangements, etc.) and would also mean that the co-owner agree and
uphold the self-same rights to the other owner party,... meaning that
if the lady cannot sign or alter her rights, then the second owner
must be willing to do the same, and contractually assign their rights
in the same manner. It will require a lot of legal wrangling, and
would be best if arranged as a partnership with assigned heirs and
rights ahead of time, and therefore deny any alteration of status to
affect the partnership, and require that all parties be willing to
agree to it. Barring such aggreement, given the taxation and estate
inheritance requirements of the UK, the easiest thing to do is set up
ownership as a separate entity, and have whomever is living there pay
rent into the ownership entity corporation, so that a defined
maintenance, tax payment and inheritance is assured.

As for the marriage, and suspicions,.... These are  not legal, estate
or ownership concerns, and would not be mentioned in relation to any
rights or ethical issues. They have no place under the concern of
anyone but the persons to be married, and need be left out of it. Find
a solicitor and place things into a fair system before prodding into
matters that are not your concern. Delving into co-mortgages, spousal
rights and issues and rights of a property needs to be dealt with
pre-need, in such matters, and not "assumed" or "handshake" agreements
which decidedly change with status, care, concern and time.

They always told me in law school that if it can't be understood by a
layman, then it isn't worth saying...