When your brother-in-law is getting married, you should give a red envelope according to your means. It is not recommended to overdo it. However, the best suggestion is to listen to your wife. After all, it is her brother's wedding, and she has the final say on how much to give. But I would suggest that the range of 5,000 to 10,000 yuan is enough.
As for gifts, I can recommend some that can be placed at home with festive meanings, such as:
Couple wedding dolls: These are the kind of soft clay dolls that can be customized based on real-life photos. You can use their wedding photos to make them
Wedding Tang suit dolls: A huggable bear wearing a Tang suit, which is very festive when placed at the bedside
Crystal music box: This is made of crystal and has the shape of a piano. The special thing is that you can photocopy their wedding photos on it
Descendant barrel: In the past, there were some customs in the south that descendants barrels were given as gifts at marriages. These are the kind of wooden barrels that come in large and small sizes, symbolizing good luck, blessings, and a large family. However, this kind of thing is no longer available, but there are similar handicrafts and ornaments
The above things are all very good. They are very festive and commemorative when placed at home. When they see these things, they will remember that they were given by their sister and brother-in-law
In addition, you can also give some cross-stitch or the like, which can be hung on the wall