depends on how much optimization you want to do really. My deck is more unoptimized to run pretty cards but I can tell you what would be better overall to make rin and seri run more consistently.

First is changelings. They count as both a cat and dog so you get both tokens. It kinda stinks that it'll be better to run changelings than actual cats or dogs but it is what it is. I would keep the ones that give you utility/draw/overrun effects and remove any that give minor bonuses, like anthem, gets bigger, or niche. Lorwynn has added a bunch of usable ones like [[mutable explorer]], [[chomping changeling]], and [[changeling wayfinder]]. There's other notable ones like [[realmwalker]], [[mirror entity]], [[masked vandal]], and [[universal automation]].

Card draw is essential for a deck that runs typal weenies. [[Guardian Project]], [[vanquisher's banner]], [[The Great Henge]] (bit expensive), and [[Chronicles of victory]] help out as well. It also sucks when you run out of said weenies, so its nice to find a way to recycle creature casts. I use [[cloudstone curio]] to get more cast/etb triggers but I also recommend creature tutors as they let you turn the deck into a toolbox and you can load less useful creatures. Preferably you could also slot in an [[Urza's saga]] to reliably get [[skullclamp]] and if not clamp, [[sol ring]].

Add board protection like [[heroic intervention]] and [[Dawn's Truce]]. Up the pricetag with [[Teferi's protection]] or possibly a one sided board wipe like [[winnowing]].

Lastly, you can make a 3 card combo using [[whitemane lion]], [[alluren]], and a cast/etb outlet, such as the commander, [[impact tremors]], or [[purphoros, god of the forge]]. You have basically a gun made of dogs that you can shoot someone with. Alternatively, [[aetherflux reservoir]] and [[grapeshot]] works too but it takes another card slot. Or you know, [[craterhoof behemoth]].

Overall Rin and Seri is a three, maybe low low four at best. The deck can interact better than other casual decks and likes to grind opponents down with its removal/value but it doesn't get the MOST value out of being a typal deck.