If the facts you have described are accurate, then simultaneous or Jr. removed link rights are probably the least of your concern about the conveyances.
Wording is key here…
Husband and wife have an undivided ½ interest, together; they are not separate.
It might depend on the state, but…the minute he dies, she still owns the ½ interest, in its entirety.
To your point, the OP states "A husband and wife have a ½ undivided interest each in three contiguous parcels." Which says to me H owns one undivided 1/2 and W the other undivided 1/2. So the scenario of H's half interest(s) being passed on to someone other than W (depending on tenancy and jurisdiction), is plausible on its face. Not sure what Jr/Sr has to do with it.