(I got bored and added this)

Sam Collins as Peter Valleyway

Peter "Pet" Valleyway

Sixteen

The oldest

Straight

He/him

Mary-Kate Olsen as Alexandra Valleyway

Alexandra Valleyway

Fourteen

The older twin / middle child

Omnisexual

She/her

Ashley Olsen as Joan Lauren Valleyway

Joan Lauren Valleyway

Fourteen

The younger twin / youngest child

Pan-demisexual

She/her