In HH there are 3 keys - one to lender, one to borrower and one to HH. You need to have 2 keys at least to move collateral. 
In Debifi 4 keys - lender, borrower, Debifi, authorized (independent) key holder. You need to have at least 3 keys to move collateral. 
If there is dispute - support aģents will solve it and co-sign with the winning party. But tbh it's rarely the case. Game theory and consensus are powerful tools 😎