Ignoring is good and remember — buns can literally take MONTHS to bond so don’t get too flustered about this taking so long.
I just brought home a fourth bun to begin bonding into my trio! As long as you help keep me strong through the bonding process, I promise to keep you strong! YOU WILL GET THIS — JUST DON’T GIVE UP!
Anyway, I would try strictly JUST stress-bonding. When they have cuddled and are doing well, progress to normal bonding. If they digress, back to stress bonding. Have you tried normal bonding in say a new house? Family member or friend who will let you borrow their living room or bathroom by chance? New area in not a stressful setting may be a good place to start after some straight stress bonding. They simply have just not worked it out yet. Don’t get down on yourself or your buns though — YOU WILL GET THIS! And when it happens, you’ll realize how much it was worth the wait. Seeing my trio cuddle and groom each other happily just melts my heart. It makes up for all the stress and time of bonding, I promise.