Equally.
Sibling 1 - working full time from age 16, has own mortgaged home, 2 children with various paid for hobbies and now both working themselves (aged mid/late teens) ie family with a work ethic! Communicates daily with parents, arranges lunches together and generally shows in interest in parents life.
Sibling 2 - reduced hours as much as possible from the birth of their first child to claim UC top ups/get as much free child care as possible. Sold their mortgaged home at the worst time and made a loss because ' they didn't like it'. Bounced around rentals and finally got into social housing. Regularly doesn't pay important bills to put the money towards socialising (getting pissed multiple times a week with their friends) neither child of this Sibling has had any kind of job (also mid/late teens), No communication with parents outside of pre arranged visits organised by Sibling 1.
Arguably Sibling 2 would benefit more from a larger share of any inheritance but that would be punishing Sibling 1 for 'doing the right thing ' all of their life and trying not to burden anyone. Sibling 1 will invest money if possible and try to make it go further for the next generation, there will be house deposits/money towards existing houses and lump sums for weddings , help with child care costs etc.
Sibling 2 will spend, spend, spend. The children will probably get a few amazing holidays out of it. Within a few years their situation will be exactly as it was pre inheritance.
Arguably, favouring the child that 'has less' will always be a lose, lose situation. Generally speaking (not including disability etc) the child with less has less for a reason, no work ethic, spending issues, alcoholism, drugs etc. Handing them a large chunk of money/estate won't suddenly better their life.