What is being smoked here? I never heard this kind of issue called right to life before.
First, per definition, "Right to Life" issues are life-and death ones where the State is presuming to authorize or permit the killing of a non-aggressor: abortion, infanticide, euthanasia, suicide, various depredations like embryo-experimentation leading to human death.
Second, these border security issues are not even equivalent. If we were talking about shooting aggressive armed people-smugglers at the border, even that's a police issue, not a right to life issue. Slavery-drug-weapons smugglers are not innocent.
But just policing your border without killing anybody, that's not even comparable in seriousness to the butchery of babies. There's certainly nothing in God's Law or Canon Law that forbids securing your national borders.
Third, these bishops are outside their competence. Public policy issues are not to be commandeered by the clergy in this fashion. Threatening canonical sanctions, that's rich. Let them calmly and factually make their case like any other citizens.
You are familiar with the Constitution?
“life, liberty and the pursuit of happiness.”
Note that life comes first!