You mentioned your wife has visit visa, for how long is it valid ?

If its valid for more than six months, you can travel to UK together and there she can apply for spouse visa. ( this is risky though )

If not ( and I would recommend ) then you apply for spouse visa in the nearest British embassy. You don't need to have a job but you will have to prove

1- You have enough money to support yourself and wife and kids without claiming any benefits.

2- You have appropriate accomodation available in the UK where you guys can live once you arrive.

( Even though these two are not as simple as they sound )

Spousa visa is issued for two years but once in UK, your wife can apply for Permanent Residence ( ILR ) straight away since you have been married for more than four years. She will just need to pass the 'Life in the UK test'.

Good luck

 

You won't find a specific amount mentioned anywhere. Just do your budgeting and see if you have enough money for all your expenses.
Rent, council taxes, bills, food etc.

You should have enough money for all your and your family's expenses for six months to be on the safe side.

Good luck !