An answer for the Tracy brothers group could also be members of the Mercury Seven, the test pilots selected to be the first astronauts. John Glenn, Alan Shepherd, Virgil (Gus) Grissom & Scott Carpenter. The Thunderbirds characters were named after them.

Enjoyed this grid.

wrong specialities for me, i'm an old lady and i don't watch the avengers. also i put monarchs as they rule in their own right, queens are more usually married to the male monarch....the king

Once you've got one group of male connections, the others are all men. The same for the women, the old fashioned names/modern names are easy to separate without knowing any connections.

It's the Scarlet Witch, with one T.

I guessed 3/4 of this and got it right. Fun grid. Thanks. :-)

Didn't accept Thunderbirds. Why??????
Didn't accept monarchs. Why???????????????