How can we come out of a lease agreement?

You can't, you have signed a legally binding agreement and unless the owner has somebody willing to take the agreement over he will hold you to the terms of the contract, no question, why would you think he will let you out of your agreement when that will cost him money?

There are always legal and financial consequences to breaking a lease. You are breaking your word and promises which legally bound you to pay rent for the term.
Try finding another tenant for the space.
Try talking with LL.

Your brother can attempt to find a sub tenant to take over the site. Your brother will be legally responsible for unpaid lease debts the subtenant does not pay.

Your brother can go to the property owner and attempt to negotiate a lease termination. In short, he offers to pay rent for a fixed period of time regardless of whether the property owner finds a new tenant or not. When the new tenant is found or the time period expires, your brother is off the hook.

Your brother can shut it down, walk away and wait for the lawsuit. If he has no assets then a lawsuit is less likely. But the property owner can't recover double rent. If the place sits vacant for 6 months and there are 36 months left on the lease, then your brother is only obligated for six months.

If this is a short term slowdown in your line of work and the future looks bright, then borrow the money from family to cover the shortfall. That is what I would attempt to do.

If you are in the UK you can walk away from it. As it is in your brothers name he is liable for the rent. If your name appears nowhere you cannot be held liable for the rent, he will then have to sell the lease on to someone else.
Sounds like that you would be classed as Managers of the shop and he is the owner. It really comes down to who signed the lease and who's name is on it.

You are going to have to read the agreement and see what the early termination clauses are from your point of view, and then do whatever is relevant.
Be aware that while you may be able to sub-let under the terms of the lease, but if you do, you may also become responsible for any debts incurred by the persons that you sub-let to.

your brother will still be held liable for the payments. Is that what you want? Try to work it out with the landlord