[nethsix]

There are 2 perspectives to be aware of: theirs & yours.

You are replacing something they wrote. That in a way is saying what they wrote is obsolete.

Ask yourself why are you and other new members are working on this project; for your own advancement or for the good of the company. If the reason is the former, there's going to be a big ego-clash.

Look for win-win: * The original team wrote the system and have learned valuable lessons from it over time. Ask them if they could write it now using current tools, how would they improve. Sell them the vision that the success of the project depends on their knowledge, and they can learn new tools, language, patterns, from the new members. * The newer members can bring new ideas (backend, UI, etc). Sell them the vision that the success of the project depends on the new skill set that they bring.

Since you cannot change the original team composition, balance it by choosing the new team carefully, e.g., choose people who are goal-driven, and result-oriented; they care more about getting things done then throwing their weight around.