Is the british royal family the most powerfull and strongest?

Yes, although not the richest, The British royal family has been ruling since 1066 (nearly 1000 years) and it has all that history to back it up, although HM Queen Elizabeth II is a highly influential individual, she is Chief Commander of the British Army, and of course she is also Queen of the following countries (known as the Commonwealth Realms)-(as well as the United Kingdom):

Canada

Australia

New Zealand

Jamaica

Barbados

The Bahamas

Grenada

Papua New Guinea

The Solomon Islands

Tuvalu

Saint Lucia

Saint Vincent and the Grenadines

Belize

Antigua and Barbuda

and Saint Kitts and Nevis

The British Royal family were most powerful at around 1919, at the Extent of the British Empire, which owned over a quarter of the Earth's land surface, making it a pre-eminent world power. At the time of the second world war, due to the damage and costs to recover Britain, the Empire lost influence and money. What's left of the British Empire are the 'Commonwealth Realms' (listed above)'. The United Kingdom is a powerful and strong country anyway, but as Head of State, it makes the Queen even more powerful. As a Queen, it by far makes more of an 'Intimidating Figure'.