In some Jain communities, “Minni” is indeed used as a family/surname.

For example:

• You can find Jain individuals with the name “Minni Jain” (where Jain is the caste/religious surname and Minni is used as a given or middle name). ( dtu.irins.org)
• There are also Jain families, especially in parts of Rajasthan and Kolkata, where “Minni” functions as a family/last name (e.g., people introduced as Sri Vinod Minni, Suresh Kumar Minni, Ashok Minni, etc.), all in clearly Jain organizational or sabha contexts. ( jainqq.org)

So:

• “Minni” is not a very common Jain surname like Shah, Jain, Kothari, Bothra, Baid, etc.
• But it does exist as a Jain family name in some sub‑communities, and also appears as part of personal names among Jains.