kevinmeiresonne said:

In the ultragrid there is the possibility to get the siblings of a certain row (row.GetSibling(....))

There is a GetSibling method on the row.

kevinmeiresonne said:

Is there an equivalent to get the sibling cell?
I need to get the cell that is shown immediately left or right of a given cell.

Not on the cell, but on the column. So you can use cell.Column.GetRelatedVisibleColumn.