Obviously you should try to avoid keeping this estate open for the next four years. The probate court will want Accountings, and in some jurisdictions, you will receive a Status Report inquiry from the probate court as to why the estate cannot be closed.
The Will should have some instruction as to disposition of the house should testator predecease the youngest son's twenty-fifth birthday. If not, it seems to me that a interpretive proceeding and possibly a request to create an estate for a term of years in the two sons be sought by way of instructions in the probate proceeding. Distribution should be made to the two adult sons as co-beneficiaries of an estate for a term of years, followed by distribution to them jointly, outright and in fee, upon that date which coincides with the youngest's 25th birthday. That proposed Order wll need to be worded carefully. Then, by the way, it won't be up to you to help refinance or deal with the property. Once the probate administration is completed, your role as Executor or Administrator of your ex-husband's estate will be over.
You do need a probate and trust lawyer to help you with this, but it should become an expense of the estate, probably would be approved as a charge against the estate, and payable by the estate. That might require a borrowing to do so, but since a refinance is anticipated anyway, seek "cash out" in addition to the refinance amount, in an amount as the Court approves for the probate attorney's fees in helping you.
Good luck with it. It is not an insurmountable problem. Unfortunate that ex-Hubby did not include a testamentary trust in his Will, which would have done all of this for you. Sometimes a simple Will is not so simple, as you can see. It may be simple for the testator and economical when executed, but that sometimes just defers the work and expense onto others later.