CathInfo.com

I make Bishop (?) Kelly's conclusion my own:

"The preponderance of the evidence, however, suggests that Archbishop Thuc was not responsible for what he did and that he had "not the full use of reason." Thus, the preponderance of the evidence indicates that he was "incapable of administering a Sacrament," as Msgr. Pohle said in The Sacraments, A Dogmatic Treatise. But since we do not know for sure, we cannot say for certain that the Thuc consecrations are invalid. Neither can we say for certain that they are valid. What we can and must say is that they are certainly doubtful as to validity. Therefore, they must be treated in the practical order as if they were certainly invalid, because when it comes to the validity of the Sacraments, it is forbidden to follow a doubtful or even a merely probable course of action. To quote Fr. Davis again:

'In conferring the Sacraments (as also in [the] Consecration in Mass) it is never allowed to adopt a probable course of action as to validity and to abandon the safer course. The contrary was explicitly condemned by Pope Innocent XI. To do so would be a grievous sin against religion, namely, an act of irreverence towards what Christ our Lord has instituted; it would be a grievous sin against charity, as the recipient would probably be deprived of the graces and effect of the Sacrament; it would be a grievous sin against justice, as the recipient has a right to valid Sacraments, whenever the minister, whether ex officio or not, undertakes to confer a Sacrament. In the necessary Sacraments,12 there is no doubt about the triple sin; in Sacraments that are not necessary, there will always be the grave sacrilege against religion.13

13.  Henry Davis, S.J., Moral and Pastoral Theology, vol. 3: Sacraments (1), 3d ed., rev. and enl. (London: Sheed & Ward, 1938), p. 27.



PS: Msgr. Pohle says:

"The combination of matter and form into a sacramental sign (confectio), and its application to the individual recipient (administratio), . . . require a minister who has the full command of reason. Hence lunatics, children, and others who have not the full use of reason are incapable of administering a Sacrament."

The Rt. Rev. Msgr. Joseph Pohle, Ph.D., D.D., The Sacraments: A Dogmatic Treatise, adapted and ed. Arthur Preuss, 3d, rev. ed., 4 vols. (St. Louis: B. Herder Book Co., 1944), vol. 1: 162.

Were these "witnesses" at the consecrations?

You are grasping at straws:

If they know a bishop is senile, they don't need to be at the consecration to hold it doubtful.

It is presumed doubtful because of the senility, since the senile cannot confect a sacrament.

"know"?  Are they doctors?

Yes.

PS: Can I know my Uncle Louie is senile if I am not a doctor?