reverse the subject/object - rheme/theme:

England & Wales only, so not Scots law:

'GFOr such reason and the aforenamed heirs (beneficiaries) of X. having succeeded (by right of rep.) to as many rights (and interests) the latter holds in such former estate, the assenting #vesting# of such goods and assets as would have to be made (future subj.) to #in# said X is to be made directly to #in# his aforementioned children in equal shares and jointly (as joint tenants)'.

"Por ello y habiendo sucedido los nombrados herederos de X, sus hijos, en cuanto(s) derechos tiene en la presente herencia aquella, la adjudicacion de bienes que hubiere de hacerse a dicha X se hara directamente a sus citados hijos por partes iguales e indiviso\"

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Note added at 20 mins (2016-10-26 08:55:54 GMT)
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For such reaason...

In my opinion, grammatically and logically it cannot refer to the "nombrados herederos" having succeeded X, but rather the children of those inheritors (I wouldn't use heirs as this refers to family members only; inheritors covers heirs, legatees and devisees), who have succeeded the inheritors of X.

If it were that case that the "nombrados herederos" have succeeded X, then grammatically it would have to read "habiéndose sucedido".
But more importantly, and logically, this couldn't be the case because then this will would not apply to their children because they would now have title to the inheritance, which they could then dispose of as they wish.
So, what it means is that if the named inheritors of X have been succeeded by their children, then X's rights in the inheritance shall go to those children (i.e. not anyone else).

My interpretation of "partes iguales e indiviso" is that it means equal parts, including any property that is undivided (real estate, ownership interests, etc.)

"Accordingly and if the designated inheritors of X have been succeeded by their children, then, insofar as the rights which X has in this inheritance, the property that would have been distributed to X shall be distributed directly to the aforementioned children as equal parts of an undivided whole".

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Note added at 6 hrs (2016-10-26 15:32:21 GMT)
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Note: I think the confusion is that there shouldn't be a comma between "X" and "sus hijos" in the ST.

Bear with me, I'm trying to work on the whole sentence...

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Note added at 28 mins (2016-10-26 09:03:15 GMT)
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I'm rather busy with my own work at the moment, but I propose something along these lines:
""Thus, the cited heirs of Mrs. X having acquired by succession the rights to this inheritance, any allocation of goods to X shall be made directly to the aforementioned children, in equal and undivided parts.""

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Note added at 29 mins (2016-10-26 09:04:22 GMT)
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NB: My suggestion is not perfect, but it's something to go on.

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Note added at 31 mins (2016-10-26 09:06:05 GMT)
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Penal Reform in England. English Studies in Criminal Science, Vol. I ...
"... It follows, for instance, that the rights acquired by succession to the estate...."

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Note added at 32 mins (2016-10-26 09:07:05 GMT)
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http://hk.lexiscn.com/law/issuance-of-the-measures-for-land-...

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Note added at 1 hr (2016-10-26 10:33:23 GMT)
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Wendy's 'beneficiaries' is a good option IMO, so I'll borrow it for this versión:
"Hence, as beneficiaries of Mrs. X, any allocation of goods to the same shall be made directly to the aforementioned children, in equal and undivided parts.""

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Note added at 3 hrs (2016-10-26 11:40:25 GMT)
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Whoever may have posted "beneficiaries" originally, I doff my translator hat to them. But I still stand by my postings.

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Note added at 3 hrs (2016-10-26 11:42:00 GMT)
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cite1
(saɪt) v.t. cit•ed, cit•ing.
1. to quote (a passage, book, author, etc.), esp. as an authority.

2. to mention in support, proof, or confirmation; refer to as an example: He cited instances of abuse.

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Note added at 8 hrs (2016-10-26 16:57:44 GMT)
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PS: If you don't Like 'cited', you could try 'said'...
PPS: Robert may be onto something, and his comment about the comma is interesting.