You sure it's got 19" wheels?That's a weird size.Might not find tires for it.Maybe there 20"?I don't think you need to"buy new".You've already got 2 of them.Give them time it needs to get them running.You'll find that they'll do fine if you are using them recreationally.Sounds like the bikes are just seized up from sitting for so long.If you get in over your head there's always
somebody here that can "talk you down"