Of course you can make a general rule. That's the purpose of Quran revealing the emphasis on kinship.
Isa (a) was the closest in terms of kinship to Yahya (a) in terms of succession of a younger person succeeding older. There could've been problems in terms of kinship if Isa (A) succeeded Zakariya (a) though because Zakariya (a) had younger siblings that might claim leadership falsely.
I am sorry i dont follow what you are saying.
John was yonger than Jesus by about 4 years.
Remember you are talking a successor must be a son, or grand son of previous prophet Jesus was not so or grandson of John. In fact Jesus was older than Yahya (John).
Beside this, Baha'u'llah had answered the correct understanding of Hadithes that talks about Mahdi being son of Hassan:
All that thou hast heard regarding Muḥammad the son of Ḥasan—may the souls of all that are immersed in the oceans of the spirit be offered up for His sake—is true beyond the shadow of
a doubt, and we all verily bear allegiance unto Him. But the imáms of the Faith have fixed His abode in the city of Jábulqá, which they have depicted in strange and marvellous signs. To interpret this city according to the literal meaning of the tradition would indeed prove impossible, nor can such a city ever be found.
Wert thou to search the uttermost corners of the earth, nay probe its length and breadth for as long as God’s eternity hath lasted and His sovereignty will endure, thou wouldst never find a city such as they have described, for the entirety of the earth could neither contain nor encompass it.
If thou wouldst lead Me unto this city, I could assuredly lead thee unto this holy Being, Whom the people have conceived according to what they possess and not to that which pertaineth unto Him! Since this is not in thy power, thou hast no recourse but to interpret symbolically the accounts and traditions that have been reported from these luminous souls.
And, as such an interpretation is needed for the traditions pertaining to the aforementioned city, so too is it required for this holy Being. When thou hast understood this interpretation, thou shalt no longer stand in need of “transformation” or aught else.
Know then that, inasmuch as all the Prophets are but one and the same soul, spirit, name, and attribute, thou must likewise see them all as bearing the name Muḥammad and as being the son of Ḥasan, as having appeared from the Jábulqá of God’s power and from the Jábulṣá of His mercy.
For by Jábulqá is meant none other than the treasure-houses of eternity in the all highest heaven and the cities of the unseen in the supernal realm. We bear witness that Muḥammad, the son of Ḥasan, was indeed in Jábulqá and appeared therefrom. Likewise, He Whom God shall make manifest abideth in that city until such time as God will have established Him upon the seat of His sovereignty. We, verily, acknowledge this truth and bear allegiance unto each and every one of them. We have chosen here to be brief in our elucidation of the meanings of Jábulqá, but if thou be of them that truly believe, thou shalt indeed comprehend all the true meanings of the mysteries enshrined within these Tablets.
But as to Him Who appeared in the year sixty, He standeth in need of neither transformation nor interpretation, for His name was Muḥammad, and He was a descendent of the Imáms of the Faith. Thus it can be truly said of Him that He was the son of Ḥasan, as is undoubtedly clear and evident unto thine eminence. Nay, He it is Who fashioned that name and created it for Himself, were ye to observe with the eye of God.
Baha'u'llah, Gems of Divine Mysteries