Nigel, the Diane Blood case a few years back invoked a similar kind of thing. However in this case husband and wife were trying for a child, and they were going to do IVF stuff, but he died (car accident?) The accident basically wiped out his brain but his body was still left (in a permanent coma) on life support. The problem then was that Mrs Blood still wanted a child, but her husband wasn't able to give consent for IVF. The reason the courts decided in favour back then was based on the husband's clearly-stated wish before he died to go through with IVF.
The difference here is that the couples have been through IVF a long time ago, and the men now don't want to go through with it for whatever reason.
"Personhood" is a term that has not been defined in law so far as I am aware. After all, is a new born baby born prematurely more of a person than a fetus in the late stages of pregnancy who may in fact be more fully developed? The significant factor in legal terms, in this country anyway, appears to be viability, the ability to survive outside the womb.
You'll find from the laws on abortion that this is *very* well-defined in law, with a cut-off on the 24th week of pregnancy. The significant factor is not viability but whether the cluster of cells in a woman's womb is able to respond to anything, or whether it's just that, a cluster of cells with potential. A 24th-week embryo can clearly not survive on its own! After that point, all foetuses have the same rights. You may disagree morally with this if you believe "personhood" begins at the moment of fertilisation or at the moment of implantation, but you can't disagree with it legally.