Short answer. Yes. An heir may sell his undivided share in the estate before partition, and the Civil Code contemplates a sale of the inheritance in bulk. What he sells is his hereditary right, not any particular house or lot, because nobody yet knows which assets will fall to him.
What the law says
One who sells an inheritance without enumerating the things of which it is composed, shall only be answerable for his character as an heir.
Civil Code, Article 1630 — Sale of an Inheritance in Bulk. Read the full provision →
What is being sold
From the moment of death an heir's right to the succession vests, but until partition he owns no identified property — he owns a fractional interest in the whole mass. That interest is transmissible, and it is what a sale of the inheritance conveys. Article 1630 addresses the version of this sale done without enumerating the things of which it is composed: no inventory, no list of titles, simply "whatever I stand to receive from my father's estate". The buyer steps into the seller's position in the settlement and takes the share as it eventually turns out to be, whether that proves larger or smaller than either of them expected.
The seller warrants only that he is an heir
This is the point of the article, and it is easy to miss. Where the sale is in bulk, the seller shall only be answerable for his character as an heir. He guarantees that he really is an heir of that decedent and that the right he transferred is his. He does not guarantee the contents or the value of the estate. If the estate turns out to be burdened by debts, if an asset the buyer assumed was there was never owned by the decedent, or if the share shrinks after the claims are paid, that is the buyer's risk. A seller who instead enumerates specific properties is making representations about them, and answers accordingly.
What the buyer does not get
A buyer of a hereditary share does not acquire the right to seize a particular lot, evict a co-heir, or have a title transferred to his name on the strength of the deed alone. He acquires the seller's place in an undivided estate, and he must wait for — and can participate in — the settlement and partition. Estate obligations come first: debts, expenses of administration and estate tax are charged against the estate before anything is distributed. The sale also cannot prejudice the legitimes of compulsory heirs, nor can one heir validly sell a specific property of the estate as if it were already his alone.
Before you sign either side of this deed
Have counsel confirm three things: that the decedent has actually died and the seller's status as heir can be documented, that the estate proceedings are properly identified, and that co-heirs are notified, since the law gives co-heirs a right to be substituted for a stranger who buys a hereditary right, on reimbursement and within a short period. Price the deal honestly against an inventory even if the deed itself enumerates nothing, and put the tax and settlement obligations in writing. A deed drafted as a sale of a specific property when the estate is still undivided invites years of litigation; the correct instrument describes what is really being sold.