Question: Can my sister’s husband hold my walima if I permit him to?
Thank you for your question.
It says in the Reliance of the Traveller:
The wedding feast is a sunna (A: whose time never expires, though it is recommended to be after intercourse). The sunna is for the meal to consist of a sheep or goat (shah, def: h2.S), though it is permissible to serve whatever food is readily available [m9.1].
It is permissible for your brother-in-law to hold your walima. I assume that by “holding“ your walima, you mean that he will pay for it and invite the guests. This is a praiseworthy act on his behalf.
Please see this article for more details:
[Ustadha] Shazia Ahmad
Checked and Approved by Shaykh Faraz Rabbani