I think someone would need to know more than what you're describing in his pulse and a family-doc's EKG to make an assessment there.
Generally speaking, very generally, people who have a PVC load >15-20% of their total beats can have some decreased function in their left ventricle measured as a decrease in ejection fraction and muscle changes. The reason they know this is that there was a study done which showed these changes reversed if the PVC load was lessened by fixing it through ablation.
If your brother is truly in 100% bigeminy he would have a 50% PVC load which is high. That would be about 50,000 PVCs per day.
Does he know the origin of the PVC? they can tell from the EKG which part of the heart they are coming from. One would need to know if they are unifocal (coming from one spot) or multifocal (coming from more than one spot).
I would wager his are originating in the RVOT (right ventricular outflow tract). The RVOT is a common hyper area, and has a higher success rate than other parts of the heart for ablation surgery because it's very accessible via catheter.
If that's his case than it would be wise to get some imaging done via an MRI or an echo, then get these done regularly over time to see if there are any changes. If there is a decrease in EF then ablation or stronger anti-arrhythmic drugs might be in order.
My humble amateur opinion is that he's young and will heal, now is the time to deal with it. Before you know it you're 50 and it's a different ballgame. Your brother is really lucky to have a caring family!