Hi and welcome
Very sorry that your piggies are touch and go.
When making any decisions you should consider:
- your space: do you have the option to provide enough space for two single cages that allow full interaction (voice, scent/pheromones and crucially full sight of body language for round the clock companionship and ongoing stimulation? If yes, then next door compansionship is an option.
- if you do not have the space for single cages next to each other and would have to keep your piggies (I assume that you are dealing with teenage boars?) on top of each other, pairing up each boar to provide the needed stimulation and companionship would be preferable.
Generally, having a character compatible mate is always better but not everybody can provide the wherewithal and compromises have to be found between space capacities/rescue dating or bonding access/neutering and bonding with a sow each option/financial capacities. The most important point for your piggies' long term mental health and quality of life is the constant access to full interaction/stimulation with their own kind.
Single Guinea Pigs - Challenges and Responsibilities
A Comprehensive Guide to Guinea Pig Boars (including a chapter on companionship and neutering/de-sexing)