You are right -Monkspath is Alderbrook catchment, not Tudor Grange. And I would think of secondaries now, as moving in a few years will be a hassle, not to mention expensive! Tg catchment houses are more expensive, so if you have your heart set on Grammar, you may not want to be paying the extra £30K
I presume you already have seen 'the map' of school catchment areas in Solihull, available to view at Solihull Connect in Solihull library (take a camera with you!). However in recent years, with a relatively low birth rate, Tudor Grange has taken in pupils out of catchment up to about 1 mile away - which does include most of Monkspath, hence the prevalence of Green uniforms there.
Alderbrook (being less popular!) has been able to offer out of catchment around 3.5 miles away, meaning many pupils in some Birmingham suburbs have been able to secure a place there. If your child was born pre-2006 and you live in the top half of Monkspath, you probably do indeed have a good chance of TG. If they were born after that, you really need to position yourself in catchment due to the birth rate rising. The TG catchment also includes outlying villages such as Hockley Heath and Tidbury Green, and these children will have priority over Monkspath children for TG. Arden is also an excellent secondary, and the schools in Knowle/Dorridge are also great. Echoing what fm has said, though, I can say pretty much all Solihull primaries are good - but they do have very different values and ethos. I moved my own children from a miserable Solihull school with very high results to one that was maybe a few points lower in the league tables and it was like moving from darkness to light... my children immediately became happier, grew in confidence, and therefore excelled far more in their new school, even though it didn't have as fancy a uniform or as stuffy an atmosphere. I would ask searching questions about their vision, parental communication, breadth of curriculum etc, rather than focus on academics. And if you are an ethnic minority (I guess not...) I would genuinely say that some Solihull primaries are far more inclusive than others.
I know little of Monkspath, (last Ofsted was satisfactory, high levels of pupil vacancies may tell a story, recent scandal linked to a male teacher can be seen in press) but I would have liked to have seen it this year, as I applied for no.4's reception place and considered it a backup. But despite 4 phone calls and promises to ring me back, I was unable to arrange a visit. Perhaps because I live in Birmingham? Other schools welcomed me to visit with no problems.