If you wanted to use that sort of construction, you would say (Loro) sono così forti come noi or (Loro) sono tanto forti quanto noi.

I had the same question

Doubtful .... Tanto means 'many' or 'lots'. Neither are mentioned in the phrase.

"forte" is the singular form for either males or females. The same happens in the plural, where "forti" is used for both genders.

'Sia...che' is the equivalent of 'either...or' or 'both...and'. For 'as...as' in Italian you can say 'tanto...quanto' or 'così...come', but you can also choose to just leave out the first half of either of those (as this sentence does).