You are leaving it a bit late to use Avios to book for July or August this year. Plus the companion voucher only allows two passengers to travel together. You'd need 2 vouchers earned on the BAPP Amex to be able to use them together for a family of 4.

Realistically 130k Aviios allows you to book for 4 people to somewhere in Europe.

Alternatively you could use some Avios to reduce the price of cash bookingboth ough that's not the best use of them.

If you want to use the companion voucher for transatlantic travel then you could book for two passengers and the pay cash for the other two.

As for searching there is Seatspy. Better to have a subscription as you are limited with the number of searches you can do without one.