If you weren't married, or party to a domestic partnership, you may not have any rights to the home (or to any other property owned by the partner). You may, however, be able to assert a "Marvin" claim. CA recognizes these types of claims, named after actor Lee Marvin, whose live-in sort of wife sued because he had given up her own acting career to act as Marvin's hostess, etc., and she claimed that he had agreed with her to treat her like a wife for property/support purposes, and that he held her out to others as his wife. The court ended up not finding for her, but did rule that 2 consenting adults who have a relationship not based solely on sex can make an agreement, like any other adults, to share property, provide support, etc. that the court would enforce.
Who holds title to the home? If just your partner, I'm afraid your partner's family, who inherit the home, can evict you, unless you can successfuly make a Marvin claim to it. If you were a joint tenant, then the home is now yours, and if you were a tenant in common, you own 1/2 the home - again, subject to any Marvin rights you may have. You seem to think you only have a right to tenancy, which may not be true.
You need to review the home title and hire a family lawyer to help you.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
I concur with the answer posted by Pamela Koslyn. The lesson here is that domestic partners can take relatively simple steps to protect their interests and the wishes of their partner and avoid the unintended hardships described in this question by (1) completing a properly executed Will (and a revocable trust in appropriate circumstances), (2) a financial power of attorney for use during a period of incapacity, and (3) an Advanced Health Care Directive to ensure the rights to direct care and visitation.
Are you on title to the property? If so, you can prevent them from entering. Did you and your partner wisely put title in your names as joint tenants with right to survivorship? If so, your partners 1/2 of the property passes to you. The same goes for your bank accounts.
If your partner did not do so, then their interest passes to their heirs. They will have to bring a probate action to obtain title. Once they do, they can bring a partition action to sell the property. Hopefully, you can afford to buy them out, as right now with the depressed market there is probably little equity in the home.
It is worth paying for an hour of legal consulting to know exactly where you stand.
I guess I wouldn’t feel lawyerly unless I wrote a disclaimer to this answer – after all, that’s what we lawyers are trained to do. So here it is. Disclaimer: Trying to provide a complete answer to a brief question without meeting the questioner and without getting all the facts is much like internet dating. Despite what you have been told by the person you’ve met online (and don’t they always put everything in the best light for themselves), once you meet them face to face you realize how much has been left out. People tend to bend the facts and there is always the other side to the story. So, this answer is about as valuable as the price that was paid for it. It should not be considered legal advice. It is meant as a general overview of how the law could apply to a very broad set of facts that may not have any applicability to the actual circumstances of the person making the question. It is hoped to provide some understanding of the broad field of law that could come into play. No attorney-client relationship has been formed with the questioner and no attorney client relationship was ever anticipated by my response to this question. I would also like to remind you that I am only licensed in the State of California, and the answer provided is based upon my knowledge of California law.