Petitioning for the boys to have their sentence reviewed and upgraded to custodial will also do nothing to bring about justice for the girls though and beyond a short term sense of relief will do nothing to address their long term trauma.
The boys were found guilty, they will have a criminal record for life, even if their conviction is spent. It will always show up on any future enhanced DBS checks. Depending on what the judge ordered, they may have to report to the police their whereabouts and will be on the sex offenders register for between 5 years and life.
Being in a Youth Offending Institute for 18months, with little access to rehabilitation support and getting into regular fights will either force them to become 'alphas' and come out with an untouchable arrogance or they will be bullied and beaten to the point where they come out with an enormous amount of resentment. Neither of those will do anything to help them understand the severity of what they did and is in fact likely to increase the likelihood of them re-offending.
Community orders like YROs, which can also result in them losing their freedom through secure orders, tagging etc are more likely to get them access to better rehabilitation services and significantly reduce the likelihood of re-offending.
If the sentence is reviewed and they are given a custodial sentence, it won't be for life - it will likely not be for more than the three years that their YRO is - maybe even less.
Calling for them to be incarcerated does nothing to help the victims and in fact increases the likelihood of re-offending and creating more victims in the future. It's mob justice.
If the concern is truly about helping the girls, it would be much more effective to use the outrage to demand that support for victims is improved.