Partner in two Firms

Yes, there is no restriction, one can be partner in unlimited no. of firms even if it pertains to same business.

Dear Mr Singh, rightly pointed by Ravikant that there is NO RESTRICTION for a person to become partner in 'n' number of firms.

Additionally, in fact, any aggrement which restricts a person to carry out a LEGAL business or profession or trade is null & void, therby, providing legal freedom to a person to become partner in multiple firms & to carry SAME trade.

Exception (for your additional knowledge only): -

However, one who has sold the goodwill of his business may agree to the buyer to not to carry on the same business in a particular local limit & for a specific time period. The condition of this agreement, if seems to the court reasonable, the person may not become partner in another firm for the same business.