go in with (someone)
To join or combine with a person or group of people to form a partnership or union. She went in with her childhood friend to open an organic bakery in their neighborhood. The Democrats and the Republicans have gone in with one another to form a truly bipartisan bill.
go in with someone (on something)
Fig. to join together with someone to work on a project; to pool financial resources with someone to buy something. I would be happy to go in with you on the charity ball. I'll find a hall. Yes, we can pool our money. I'll go in with you.