Found: mercenary who has two stepchildren hired by an old woman in a wheelchair to avenge the death of her daughter in africa

I remember very little of the book, so I will make the points that I remember:

1- the book begins with a sniper who is observing a camping tent, sees that a girl comes out and then a boy and kills them both.

2- the girl was the daughter of an older woman with a lot of money, and who was in a wheelchair

3- the lady in the wheelchair hires a famous mercenary (I think he had scars on his face) this mercenary becomes one of the protagonists of the story

4- the mercenary has two stepchildren, and lives in a country in a house that overlooks a cliff or something like that

5- in a part of the book when the mercenary accepts the mission, he goes on a plane and the lady in a wheelchair insists on going with them and yes, he goes with them,

6- the lady in the wheelchair becomes fond of the mercenary's stepdaughter

7- the mercenary's mission focuses on Africa more than anything

8- the mercenary at one point in the book looks for a friend to help him and there is a part in which he places a pair of boots at the ends of some sticks to make false footprints and mislead the enemies .......

well that's the only thing I can remember about the book .....
the book had a white cover ..... a medium book of about 300 pages more or less

I don't remember the author of that book, I read it like ten or twelve years ago.
please help me yes I have like three years looking and nothing
And what I do remember very well is that I liked the book very much so I don't understand how I forgot the title and the author, what a true madness =) .........

Ready I found it, it's called "The avenger" by A.J. Quinnell

I can't find a touchstone for the title, but here is the author:

A. J. Quinnell