They can foreclose if you fall behind on your payments. HELOC is secured by the property you live in, even though the note is in your deceased husband's name. Maybe you can refinance or modify the first mortgage to lower your monthly payments. If you can't afford an attorney, you would contact the lender to ask for modification. You can also contact the lender for refinance, or contact another lender or a mortgage broker for a refinance.
Please note that the above is not intended as legal advice, it is for educational purposes only. No attorney-client relationship is created or is or is intended to be created by my answer. You should contact an attorney in your area to discuss your case.
If you signed the mortgage document consenting to imposition of a lien on your homestead, which from your question appears to be the case, then even if you are not personally responsible for repayment of the debt, the HELOC creditor has the right to foreclose on it if it does not receive payment. However,whether it has the right is not the same as whether it would actually do that - that depends on the financial considerations. If the mortgage debt on the first mortgage exceeds the value of the property, most second mortgage creditors realize that a foreclosure would gain them nothing,m and would cause them to incur cost for no economic benefit.
While you say you can't afford a lawyer, it is important that you understand that there may be some solution to this problem, but that only a lawyer knowledgable in this sort of problem would be able to help you to sort it out. If you can't continue making the payment on the second, it is inevitably going to hit the wall. That is why it is critical that you get completent legal advice and assistance to analyze your situation and to develop a strategy, so that that does not happen.
On a publicn web site, all that is possible is to explain generalities to people. Every case is different. For case-specific legal advice, only a one on one analysis with a knowledgable attorney will uncover potential strategies geared to your specific situation.
Please note that the above is not intended as legal advice, it is for educational purposes only. No attorney-client relationship is created or is intended to be created hereby. You should contact a local attorney to discuss and to obtain legal advice.