I think that Elizabeth and Anne's financial future was secure. Even if they would not be as wealthy after Sir Walter dies than before.

There's no reference to them being poor, though in most of the other novels JA makes the precarious situations of her heroines particularly clear. And it does appear to have been customary, on marriage, for lawyers to secure the incomes of any children in marriage settlements. Apart from the risk of a spendthrift in the marriage, it was sensible to guard against the husband dying, the wife re-marrying a scoundrel, who would gain control of the family money and disinherit the first husband's children. And of course, if the deeds just say "10,000 to each child" then it would be easy enough for the scoundrel to spend the 10,000 and disinherit them that way, so it makes sense for lawyers to put the amount for each child in a trust and give the parents the rights to the income.

In NA, General Tilney can't disinherit Henry for wanting to marry Catherine due to marriage settlements, in P&P although the Longbourne estate was entailed, Mrs Bennets' dowry appears to have been settled on their children (the proportion to each to be determined by the parents).