I can't really understand the difference between Lives and LivesLeft. In my humble opinion, it should be like this:

[pascal]
procedure TFormGame.BonusLife;
begin
case Points of
25000: Inc(Lives, 2); // or Lives := Lives + 2;
50000: Inc(Lives, 2); // or Lives := Lives + 2;
end;
end;
[/pascal]

This procedure should be constantly performed (i.e. in OnTimer event).

And a side note: change the name Lives on Lifes.

Hope that helped a bit.