when there are more than 4 avatar I constantly crashes

[TheHotAngel]

when there are more than 4 avatar I constantly crashes

[Rolig Loon]

Either your computer barely meets the minimum requirements for Second Life or you have an unreliable Internet connection, or both.  Second Life normally puts a heavy demand on your computer's graphics card.  When it has to deal with rendering extra avatars, high resolution images, and mesh clothing that has excessive detail, the extra load can be too much.  To prevent it from overheating and damaging expensive components, your computer simply shuts down the viewer.

At a minimum, reduce your draw distance (in Preferences >>> Graphics) to 64m or less, and drop your Quality slider one or two full steps (to Moderate or lower).  Decrease the number of non-imposter avatars from its default (7) to 3 or 4. Lower your viewer's Maximum Complexity setting (in Preferences >> Graphics >> Advanced Settings). If you are using a wireless Internet connection, don't.  Switch to a DSL or cable connection.  Reboot both your router and your modem.

Read https://community.secondlife.com/t5/English-Knowledge-Base/Avatar-Rendering-Complexity/ta-p/2967838    and

https://community.secondlife.com/t5/English-Knowledge-Base/How-to-improve-Viewer-performance/ta-p/1316923